When it comes to measuring the accuracy of your Rolex, most people just compare their watch with the an atomic timer on their computer, mobile phone, or by dialing “popcorn.” While checking your Rolex against a reliable clock is a quick and dirty method, measuring “time drift” over a period takes a few days of documentation.


Fortunately, there are a couple of apps that make measuring time drift fairly painless.


Two apps I find useful is WatchTracker for iOS on the iPhone and WatchDrift for MacOS. Today I will cover WatchTracker for iOS and next week I’ll show you WatchDrift.  WatchTracker is a great little $4.99 app that runs on iOS 5.0 or later. It weighs in at a paltry 300k but it does what it is intended to do very well.  Essentially, WatchTracker pings atomic time and calibrates a reference clock on your screen, then it asks for the time on your Rolex 10 – 15 seconds prior to when you Rolex is at that time.  When your Rolex hits the time shown on screen, you tap the screen to enter the Rolex’s exact time.  By giving you a 10-15 second lead time, you can enter this data point precisely.



These next features are what set WatchTracker apart from the simple calibrating your Rolex from atomic time. After entering a data point, WatchTracker saves it until you run the application again and set another data point. Normally, I put in a data point every 24-36 hours.  Over the course of a month, WatchTracker calculates how much time drift your watch has. Additionally, WatchTracker creates a chart to show time drift visually.  Because movement and gravity affect the balance spring inside your Rolex, the amount of time gained or lost within a 24 hour period varies each day. A watch that went cycling, golfing, or some type of outdoor adventure will have a different rate than a watch that was doing desk-diving duty at the office.  Even though your Rolex might gain/lose time each day, the amount of gain/loss averaged over days gives you a better accuracy reading.  This is one of the reasons why Contrôle Officiel Suisse des Chronomètres (COSC) chronometer certification lasts 10 days in various conditions rather than doing a simple time reading against accurate reference time.



The other advantage WatchTracker brings is the ability to track multiple watches.  While there might be a one watch on your wrist, many people own multiple watches.  WatchTracker will help you track time drift on all your watches, including non-Rolex watches and quartz watches.



Measuring your watch or clock against a known good clock is an age-old tradition that goes back to watching the ball drop every day at noon on the Greenwich observatory for ship clocks to synchronize against known accurate time.  The ball dropping at Greenwich is where the Time Square / New Years ball drop on New Year Eve is based.  Rather than waiting for balls to drop, or calling “popcorn” on your landline, use the computing power on your iPhone. The app is less than five bucks, is stable, uses the standard Apple iOS interface, and is available on iTunes at

– Sheldon Smith