diff --git a/src/chronometer.js b/src/chronometer.js
index 83c75bd2..6a498491 100644
--- a/src/chronometer.js
+++ b/src/chronometer.js
@@ -1,33 +1,54 @@
 class Chronometer {
   constructor() {
     // ... your code goes here
+    this.currentTime = 0;
+    this.intervalId = null;
   }
 
   start(printTimeCallback) {
     // ... your code goes here
+    if (this.intervalId) return;
+
+    this.intervalId = setInterval(() => {
+      this.currentTime++;
+
+      if (printTimeCallback) {
+        printTimeCallback();
+      }
+    }, 1000);
   }
 
   getMinutes() {
     // ... your code goes here
+    return Math.floor(this.currentTime / 60);
   }
 
   getSeconds() {
     // ... your code goes here
+    return this.currentTime % 60;
   }
 
   computeTwoDigitNumber(value) {
     // ... your code goes here
+    return String(value).padStart(2, "0");
   }
 
   stop() {
     // ... your code goes here
+    clearInterval(this.intervalId);
+    this.intervalId = null;
   }
 
   reset() {
     // ... your code goes here
+    this.currentTime = 0;
   }
 
   split() {
     // ... your code goes here
+    const minutes = this.computeTwoDigitNumber(this.getMinutes());
+    const seconds = this.computeTwoDigitNumber(this.getSeconds());
+
+    return `${minutes}:${seconds}`;
   }
 }