diff --git a/src/Duration.ts b/src/Duration.ts
new file mode 100644
index 0000000..117d501
--- /dev/null
+++ b/src/Duration.ts
@@ -0,0 +1,7 @@
+export class Duration {
+  constructor(readonly value: number) {}
+
+  add(other: Duration): Duration {
+    return new Duration(this.value + other.value);
+  }
+}
diff --git a/src/Seconds.ts b/src/Seconds.ts
deleted file mode 100644
index 127bb44..0000000
--- a/src/Seconds.ts
+++ /dev/null
@@ -1,7 +0,0 @@
-export class Seconds {
-  constructor(readonly value: number) {}
-
-  add(other: Seconds): Seconds {
-    return new Seconds(this.value + other.value);
-  }
-}
diff --git a/src/ast.ts b/src/ast.ts
index 9c57a16..9862dad 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -1,5 +1,5 @@
 import { IntervalType } from "./parser/tokenizer";
-import { Seconds } from "./Seconds";
+import { Duration } from "./Duration";
 
 export type Workout = {
   name: string;
@@ -10,13 +10,13 @@ export type Workout = {
 
 export type Interval = {
   type: IntervalType;
-  duration: Seconds;
+  duration: Duration;
   intensity: { from: number; to: number };
   cadence?: number;
   comments: Comment[];
 };
 
 export type Comment = {
-  offset: Seconds;
+  offset: Duration;
   text: string;
 };
diff --git a/src/detectRepeats.test.ts b/src/detectRepeats.test.ts
index 0ecd29a..176e93d 100644
--- a/src/detectRepeats.test.ts
+++ b/src/detectRepeats.test.ts
@@ -1,6 +1,6 @@
 import { Interval } from "./ast";
 import { detectRepeats } from "./detectRepeats";
-import { Seconds } from "./Seconds";
+import { Duration } from "./Duration";
 
 describe("detectRepeats()", () => {
   it("does nothing with empty array", () => {
@@ -9,32 +9,32 @@ describe("detectRepeats()", () => {
 
   it("does nothing when no interval repeats", () => {
     const intervals: Interval[] = [
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(60), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Interval", duration: new Seconds(30), intensity: { from: 1.2, to: 1.2 }, comments: [] },
-      { type: "Cooldown", duration: new Seconds(60), intensity: { from: 1, to: 0.5 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(60), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Interval", duration: new Duration(30), intensity: { from: 1.2, to: 1.2 }, comments: [] },
+      { type: "Cooldown", duration: new Duration(60), intensity: { from: 1, to: 0.5 }, comments: [] },
     ];
     expect(detectRepeats(intervals)).toEqual(intervals);
   });
 
   it("detects whole workout consisting of repetitions", () => {
     const intervals: Interval[] = [
-      { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
     ];
     expect(detectRepeats(intervals)).toEqual([
       {
         type: "repeat",
         times: 4,
         intervals: [
-          { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, comments: [] },
-          { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+          { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, comments: [] },
+          { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
         ],
         comments: [],
       },
@@ -43,54 +43,54 @@ describe("detectRepeats()", () => {
 
   it("detects repetitions in the middle of workout", () => {
     const intervals: Interval[] = [
-      { type: "Warmup", duration: new Seconds(60), intensity: { from: 0.5, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(120), intensity: { from: 0.2, to: 0.2 }, comments: [] },
-      { type: "Interval", duration: new Seconds(60), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(60), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(60), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(60), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Rest", duration: new Seconds(120), intensity: { from: 0.2, to: 0.2 }, comments: [] },
-      { type: "Cooldown", duration: new Seconds(60), intensity: { from: 1, to: 0.5 }, comments: [] },
+      { type: "Warmup", duration: new Duration(60), intensity: { from: 0.5, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(120), intensity: { from: 0.2, to: 0.2 }, comments: [] },
+      { type: "Interval", duration: new Duration(60), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(60), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(60), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(60), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Rest", duration: new Duration(120), intensity: { from: 0.2, to: 0.2 }, comments: [] },
+      { type: "Cooldown", duration: new Duration(60), intensity: { from: 1, to: 0.5 }, comments: [] },
     ];
     expect(detectRepeats(intervals)).toEqual([
-      { type: "Warmup", duration: new Seconds(60), intensity: { from: 0.5, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(120), intensity: { from: 0.2, to: 0.2 }, comments: [] },
+      { type: "Warmup", duration: new Duration(60), intensity: { from: 0.5, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(120), intensity: { from: 0.2, to: 0.2 }, comments: [] },
       {
         type: "repeat",
         times: 4,
         intervals: [
-          { type: "Interval", duration: new Seconds(60), intensity: { from: 1, to: 1 }, comments: [] },
-          { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+          { type: "Interval", duration: new Duration(60), intensity: { from: 1, to: 1 }, comments: [] },
+          { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
         ],
         comments: [],
       },
-      { type: "Rest", duration: new Seconds(120), intensity: { from: 0.2, to: 0.2 }, comments: [] },
-      { type: "Cooldown", duration: new Seconds(60), intensity: { from: 1, to: 0.5 }, comments: [] },
+      { type: "Rest", duration: new Duration(120), intensity: { from: 0.2, to: 0.2 }, comments: [] },
+      { type: "Cooldown", duration: new Duration(60), intensity: { from: 1, to: 0.5 }, comments: [] },
     ]);
   });
 
   it("detects multiple repetitions", () => {
     const intervals: Interval[] = [
-      { type: "Interval", duration: new Seconds(60), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(60), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(100), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(100), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(100), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(100), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(60), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(60), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(100), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(100), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(100), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(100), intensity: { from: 0.5, to: 0.5 }, comments: [] },
     ];
     expect(detectRepeats(intervals)).toEqual([
       {
         type: "repeat",
         times: 2,
         intervals: [
-          { type: "Interval", duration: new Seconds(60), intensity: { from: 1, to: 1 }, comments: [] },
-          { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+          { type: "Interval", duration: new Duration(60), intensity: { from: 1, to: 1 }, comments: [] },
+          { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
         ],
         comments: [],
       },
@@ -98,8 +98,8 @@ describe("detectRepeats()", () => {
         type: "repeat",
         times: 2,
         intervals: [
-          { type: "Interval", duration: new Seconds(100), intensity: { from: 1, to: 1 }, comments: [] },
-          { type: "Rest", duration: new Seconds(100), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+          { type: "Interval", duration: new Duration(100), intensity: { from: 1, to: 1 }, comments: [] },
+          { type: "Rest", duration: new Duration(100), intensity: { from: 0.5, to: 0.5 }, comments: [] },
         ],
         comments: [],
       },
@@ -108,22 +108,22 @@ describe("detectRepeats()", () => {
 
   it("takes cadence differences into account", () => {
     const intervals: Interval[] = [
-      { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
-      { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, cadence: 100, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, cadence: 80, comments: [] },
-      { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, cadence: 100, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, cadence: 80, comments: [] },
+      { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, cadence: 100, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, cadence: 80, comments: [] },
+      { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, cadence: 100, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, cadence: 80, comments: [] },
     ];
     expect(detectRepeats(intervals)).toEqual([
-      { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, comments: [] },
-      { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+      { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, comments: [] },
+      { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, comments: [] },
       {
         type: "repeat",
         times: 2,
         intervals: [
-          { type: "Interval", duration: new Seconds(120), intensity: { from: 1, to: 1 }, cadence: 100, comments: [] },
-          { type: "Rest", duration: new Seconds(60), intensity: { from: 0.5, to: 0.5 }, cadence: 80, comments: [] },
+          { type: "Interval", duration: new Duration(120), intensity: { from: 1, to: 1 }, cadence: 100, comments: [] },
+          { type: "Rest", duration: new Duration(60), intensity: { from: 0.5, to: 0.5 }, cadence: 80, comments: [] },
         ],
         comments: [],
       },
@@ -132,14 +132,14 @@ describe("detectRepeats()", () => {
 
   it("does not consider warmup/cooldown-range intervals to be repeatable", () => {
     const intervals: Interval[] = [
-      { type: "Warmup", duration: new Seconds(60), intensity: { from: 0.1, to: 1 }, comments: [] },
-      { type: "Cooldown", duration: new Seconds(120), intensity: { from: 1, to: 0.5 }, comments: [] },
-      { type: "Warmup", duration: new Seconds(60), intensity: { from: 0.1, to: 1 }, comments: [] },
-      { type: "Cooldown", duration: new Seconds(120), intensity: { from: 1, to: 0.5 }, comments: [] },
-      { type: "Warmup", duration: new Seconds(60), intensity: { from: 0.1, to: 1 }, comments: [] },
-      { type: "Cooldown", duration: new Seconds(120), intensity: { from: 1, to: 0.5 }, comments: [] },
-      { type: "Warmup", duration: new Seconds(60), intensity: { from: 0.1, to: 1 }, comments: [] },
-      { type: "Cooldown", duration: new Seconds(120), intensity: { from: 1, to: 0.5 }, comments: [] },
+      { type: "Warmup", duration: new Duration(60), intensity: { from: 0.1, to: 1 }, comments: [] },
+      { type: "Cooldown", duration: new Duration(120), intensity: { from: 1, to: 0.5 }, comments: [] },
+      { type: "Warmup", duration: new Duration(60), intensity: { from: 0.1, to: 1 }, comments: [] },
+      { type: "Cooldown", duration: new Duration(120), intensity: { from: 1, to: 0.5 }, comments: [] },
+      { type: "Warmup", duration: new Duration(60), intensity: { from: 0.1, to: 1 }, comments: [] },
+      { type: "Cooldown", duration: new Duration(120), intensity: { from: 1, to: 0.5 }, comments: [] },
+      { type: "Warmup", duration: new Duration(60), intensity: { from: 0.1, to: 1 }, comments: [] },
+      { type: "Cooldown", duration: new Duration(120), intensity: { from: 1, to: 0.5 }, comments: [] },
     ];
     expect(detectRepeats(intervals)).toEqual(intervals);
   });
@@ -148,41 +148,41 @@ describe("detectRepeats()", () => {
     const intervals: Interval[] = [
       {
         type: "Interval",
-        duration: new Seconds(100),
+        duration: new Duration(100),
         intensity: { from: 1, to: 1 },
         comments: [
-          { offset: new Seconds(0), text: "Let's start" },
-          { offset: new Seconds(20), text: "Stay strong!" },
-          { offset: new Seconds(90), text: "Finish it!" },
+          { offset: new Duration(0), text: "Let's start" },
+          { offset: new Duration(20), text: "Stay strong!" },
+          { offset: new Duration(90), text: "Finish it!" },
         ],
       },
       {
         type: "Rest",
-        duration: new Seconds(100),
+        duration: new Duration(100),
         intensity: { from: 0.5, to: 0.5 },
         comments: [
-          { offset: new Seconds(0), text: "Huh... have a rest" },
-          { offset: new Seconds(80), text: "Ready for next?" },
+          { offset: new Duration(0), text: "Huh... have a rest" },
+          { offset: new Duration(80), text: "Ready for next?" },
         ],
       },
       {
         type: "Interval",
-        duration: new Seconds(100),
+        duration: new Duration(100),
         intensity: { from: 1, to: 1 },
         comments: [
-          { offset: new Seconds(0), text: "Bring it on again!" },
-          { offset: new Seconds(50), text: "Half way" },
-          { offset: new Seconds(90), text: "Almost there!" },
+          { offset: new Duration(0), text: "Bring it on again!" },
+          { offset: new Duration(50), text: "Half way" },
+          { offset: new Duration(90), text: "Almost there!" },
         ],
       },
       {
         type: "Rest",
-        duration: new Seconds(100),
+        duration: new Duration(100),
         intensity: { from: 0.5, to: 0.5 },
         comments: [
-          { offset: new Seconds(30), text: "Wow... you did it!" },
-          { offset: new Seconds(40), text: "Nice job." },
-          { offset: new Seconds(50), text: "Until next time..." },
+          { offset: new Duration(30), text: "Wow... you did it!" },
+          { offset: new Duration(40), text: "Nice job." },
+          { offset: new Duration(50), text: "Until next time..." },
         ],
       },
     ];
@@ -191,24 +191,24 @@ describe("detectRepeats()", () => {
         type: "repeat",
         times: 2,
         intervals: [
-          { type: "Interval", duration: new Seconds(100), intensity: { from: 1, to: 1 }, comments: [] },
-          { type: "Rest", duration: new Seconds(100), intensity: { from: 0.5, to: 0.5 }, comments: [] },
+          { type: "Interval", duration: new Duration(100), intensity: { from: 1, to: 1 }, comments: [] },
+          { type: "Rest", duration: new Duration(100), intensity: { from: 0.5, to: 0.5 }, comments: [] },
         ],
         comments: [
-          { offset: new Seconds(0), text: "Let's start" },
-          { offset: new Seconds(20), text: "Stay strong!" },
-          { offset: new Seconds(90), text: "Finish it!" },
+          { offset: new Duration(0), text: "Let's start" },
+          { offset: new Duration(20), text: "Stay strong!" },
+          { offset: new Duration(90), text: "Finish it!" },
 
-          { offset: new Seconds(100), text: "Huh... have a rest" },
-          { offset: new Seconds(180), text: "Ready for next?" },
+          { offset: new Duration(100), text: "Huh... have a rest" },
+          { offset: new Duration(180), text: "Ready for next?" },
 
-          { offset: new Seconds(200), text: "Bring it on again!" },
-          { offset: new Seconds(250), text: "Half way" },
-          { offset: new Seconds(290), text: "Almost there!" },
+          { offset: new Duration(200), text: "Bring it on again!" },
+          { offset: new Duration(250), text: "Half way" },
+          { offset: new Duration(290), text: "Almost there!" },
 
-          { offset: new Seconds(330), text: "Wow... you did it!" },
-          { offset: new Seconds(340), text: "Nice job." },
-          { offset: new Seconds(350), text: "Until next time..." },
+          { offset: new Duration(330), text: "Wow... you did it!" },
+          { offset: new Duration(340), text: "Nice job." },
+          { offset: new Duration(350), text: "Until next time..." },
         ],
       },
     ]);
diff --git a/src/detectRepeats.ts b/src/detectRepeats.ts
index 9652c1e..3a0376a 100644
--- a/src/detectRepeats.ts
+++ b/src/detectRepeats.ts
@@ -1,6 +1,6 @@
 import { eqProps, flatten, zip } from "ramda";
 import { Interval, Comment } from "./ast";
-import { Seconds } from "./Seconds";
+import { Duration } from "./Duration";
 
 export type RepeatedInterval = {
   type: "repeat";
@@ -32,7 +32,7 @@ const countRepetitions = (reference: Interval[], intervals: Interval[], startInd
   return repeats;
 };
 
-const offsetComments = (interval: Interval, baseOffset: Seconds): Comment[] => {
+const offsetComments = (interval: Interval, baseOffset: Duration): Comment[] => {
   return interval.comments.map(({ offset, ...rest }) => ({
     offset: baseOffset.add(offset),
     ...rest,
@@ -40,7 +40,7 @@ const offsetComments = (interval: Interval, baseOffset: Seconds): Comment[] => {
 };
 
 const collectComments = (intervals: Interval[]): Comment[] => {
-  let previousIntervalsDuration = new Seconds(0);
+  let previousIntervalsDuration = new Duration(0);
   return flatten(
     intervals.map((interval) => {
       const comments = offsetComments(interval, previousIntervalsDuration);
diff --git a/src/parser/parser.test.ts b/src/parser/parser.test.ts
index 8da3c2d..51c939e 100644
--- a/src/parser/parser.test.ts
+++ b/src/parser/parser.test.ts
@@ -71,7 +71,7 @@ Rest: 5:00 45%
         Object {
           "cadence": undefined,
           "comments": Array [],
-          "duration": Seconds {
+          "duration": Duration {
             "value": 300,
           },
           "intensity": Object {
@@ -83,7 +83,7 @@ Rest: 5:00 45%
         Object {
           "cadence": 90,
           "comments": Array [],
-          "duration": Seconds {
+          "duration": Duration {
             "value": 600,
           },
           "intensity": Object {
@@ -95,7 +95,7 @@ Rest: 5:00 45%
         Object {
           "cadence": undefined,
           "comments": Array [],
-          "duration": Seconds {
+          "duration": Duration {
             "value": 300,
           },
           "intensity": Object {
@@ -136,7 +136,7 @@ Interval: 5:00 50%
           Object {
             "cadence": undefined,
             "comments": Array [],
-            "duration": Seconds {
+            "duration": Duration {
               "value": 300,
             },
             "intensity": Object {
@@ -148,7 +148,7 @@ Interval: 5:00 50%
           Object {
             "cadence": undefined,
             "comments": Array [],
-            "duration": Seconds {
+            "duration": Duration {
               "value": 600,
             },
             "intensity": Object {
@@ -160,7 +160,7 @@ Interval: 5:00 50%
           Object {
             "cadence": undefined,
             "comments": Array [],
-            "duration": Seconds {
+            "duration": Duration {
               "value": 300,
             },
             "intensity": Object {
@@ -188,7 +188,7 @@ Cooldown: 5:30 70%..45%
         Object {
           "cadence": 100,
           "comments": Array [],
-          "duration": Seconds {
+          "duration": Duration {
             "value": 330,
           },
           "intensity": Object {
@@ -200,7 +200,7 @@ Cooldown: 5:30 70%..45%
         Object {
           "cadence": undefined,
           "comments": Array [],
-          "duration": Seconds {
+          "duration": Duration {
             "value": 330,
           },
           "intensity": Object {
@@ -232,7 +232,7 @@ Cooldown: 5:30 70%..45%
       Object {
         "cadence": undefined,
         "comments": Array [],
-        "duration": Seconds {
+        "duration": Duration {
           "value": 10,
         },
         "intensity": Object {
@@ -246,7 +246,7 @@ Cooldown: 5:30 70%..45%
       Object {
         "cadence": 100,
         "comments": Array [],
-        "duration": Seconds {
+        "duration": Duration {
           "value": 10,
         },
         "intensity": Object {
@@ -260,7 +260,7 @@ Cooldown: 5:30 70%..45%
       Object {
         "cadence": 100,
         "comments": Array [],
-        "duration": Seconds {
+        "duration": Duration {
           "value": 10,
         },
         "intensity": Object {
@@ -277,7 +277,7 @@ Cooldown: 5:30 70%..45%
       Object {
         "cadence": 100,
         "comments": Array [],
-        "duration": Seconds {
+        "duration": Duration {
           "value": 10,
         },
         "intensity": Object {
@@ -291,7 +291,7 @@ Cooldown: 5:30 70%..45%
       Object {
         "cadence": 100,
         "comments": Array [],
-        "duration": Seconds {
+        "duration": Duration {
           "value": 10,
         },
         "intensity": Object {
@@ -373,37 +373,37 @@ Rest: 5:00 50%
             "cadence": undefined,
             "comments": Array [
               Object {
-                "offset": Seconds {
+                "offset": Duration {
                   "value": 0,
                 },
                 "text": "Find your rythm.",
               },
               Object {
-                "offset": Seconds {
+                "offset": Duration {
                   "value": 60,
                 },
                 "text": "Try to settle in for the effort",
               },
               Object {
-                "offset": Seconds {
+                "offset": Duration {
                   "value": 300,
                 },
                 "text": "Half way through",
               },
               Object {
-                "offset": Seconds {
+                "offset": Duration {
                   "value": 540,
                 },
                 "text": "Almost there",
               },
               Object {
-                "offset": Seconds {
+                "offset": Duration {
                   "value": 570,
                 },
                 "text": "Final push. YOU GOT IT!",
               },
             ],
-            "duration": Seconds {
+            "duration": Duration {
               "value": 600,
             },
             "intensity": Object {
@@ -416,19 +416,19 @@ Rest: 5:00 50%
             "cadence": undefined,
             "comments": Array [
               Object {
-                "offset": Seconds {
+                "offset": Duration {
                   "value": 0,
                 },
                 "text": "Great effort!",
               },
               Object {
-                "offset": Seconds {
+                "offset": Duration {
                   "value": 30,
                 },
                 "text": "Cool down well after all of this.",
               },
             ],
-            "duration": Seconds {
+            "duration": Duration {
               "value": 300,
             },
             "intensity": Object {
diff --git a/src/parser/parser.ts b/src/parser/parser.ts
index ae6d871..a9a7a2a 100644
--- a/src/parser/parser.ts
+++ b/src/parser/parser.ts
@@ -1,5 +1,5 @@
 import { Interval, Workout, Comment } from "../ast";
-import { Seconds } from "../Seconds";
+import { Duration } from "../Duration";
 import { ParseError } from "./ParseError";
 import { SourceLocation, Token } from "./tokenizer";
 
@@ -66,7 +66,7 @@ const parseIntervalComments = (tokens: Token[]): [Comment[], Token[]] => {
         throw new ParseError(`Expected [comment text] instead got ${tokenToString(text)}`, text?.loc || offset.loc);
       }
       comments.push({
-        offset: new Seconds(offset.value),
+        offset: new Duration(offset.value),
         text: text.value,
       });
       tokens = rest;
@@ -85,7 +85,7 @@ const parseIntervalParams = (tokens: Token[], loc: SourceLocation): [IntervalDat
   while (tokens[0]) {
     const token = tokens[0];
     if (token.type === "duration") {
-      data.duration = new Seconds(token.value);
+      data.duration = new Duration(token.value);
       tokens.shift();
     } else if (token.type === "cadence") {
       data.cadence = token.value;
diff --git a/src/stats/totalDuration.ts b/src/stats/totalDuration.ts
index 284ca74..33fafe8 100644
--- a/src/stats/totalDuration.ts
+++ b/src/stats/totalDuration.ts
@@ -1,5 +1,5 @@
 import { Interval } from "../ast";
-import { Seconds } from "../Seconds";
+import { Duration } from "../Duration";
 
-export const totalDuration = (intervals: Interval[]): Seconds =>
-  intervals.reduce((total, interval) => total.add(interval.duration), new Seconds(0));
+export const totalDuration = (intervals: Interval[]): Duration =>
+  intervals.reduce((total, interval) => total.add(interval.duration), new Duration(0));
diff --git a/src/stats/tss.ts b/src/stats/tss.ts
index d795855..6cc5a76 100644
--- a/src/stats/tss.ts
+++ b/src/stats/tss.ts
@@ -1,5 +1,5 @@
 import { Interval } from "../ast";
-import { Seconds } from "../Seconds";
+import { Duration } from "../Duration";
 
 // Training Stress Score formula from Training and Racing with a Power Meter:
 //
@@ -9,13 +9,13 @@ import { Seconds } from "../Seconds";
 // W - power in watts
 // IF - intensity factor (power / FTP)
 
-const steadyTss = (duration: Seconds, intensity: number): number => {
+const steadyTss = (duration: Duration, intensity: number): number => {
   return ((duration.value * intensity * intensity) / 3600) * 100;
 };
 
-const rangeTss = (duration: Seconds, from: number, to: number): number => {
+const rangeTss = (duration: Duration, from: number, to: number): number => {
   let score = 0;
-  const step = new Seconds(1);
+  const step = new Duration(1);
   for (let i = 0; i < duration.value; i += step.value) {
     const intensity = from + (to - from) * (i / duration.value);
     score += steadyTss(step, intensity);
diff --git a/src/stats/tss2.ts b/src/stats/tss2.ts
index da0802b..9d3c7b6 100644
--- a/src/stats/tss2.ts
+++ b/src/stats/tss2.ts
@@ -1,4 +1,4 @@
-import { Seconds } from "../Seconds";
+import { Duration } from "../Duration";
 
 // Training Stress Score formula from Training and Racing with a Power Meter:
 //
@@ -13,6 +13,6 @@ import { Seconds } from "../Seconds";
 // TSS = (s * (FTP * IF) * IF) / (FTP * 3600) * 100
 // TSS = (s * IF * IF) / 3600 * 100
 
-export const tss2 = (duration: Seconds, intensity: number): number => {
+export const tss2 = (duration: Duration, intensity: number): number => {
   return ((duration.value * intensity * intensity) / 3600) * 100;
 };