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You may have noticed that ring of numbers outside of the regular dial on your sports watch, but fewer and fewer people know how to use it. This dial is known as the tachymeter, and it used to be a standard feature of most analog watches. Today, fewer watches come with a tachymeter, and it has become more of a decoration than a utility feature. However, if you're constantly trying to figure out speed, frequency of repetition or other similar functions, your tachymeter could be a handy tool that will save you quite a bit of mental math.

**What is a tachymeter?**

Essentially, a tachymeter shows you how many times something will happen in an hour. If you want to know the rate per hour of any action, simply note how many seconds it takes to complete that action and then note the reading on the tachymeter. With a few minor mental calculations, you can use this number to ascertain repetitions of actions that take minutes rather than seconds.

**How tachymeters work**

The basis of the tachymeter is a simple equation that takes 3,600 (the number of seconds in an hour) divided by the seconds in the action you wish to measure, which equals your tachymeter time. For example, if you are able to stuff, seal and address an envelope in nine seconds, this calculation informs you that you can stuff 400 envelopes in an hour. If you're wearing an analog watch equipped with a tachymeter, the second hand will point directly to the 400 on the tachymeter dial.

If the action actually took you nine minutes, then you would divide this number by sixty to determine that you can do just under seven every hour. Runners use this to measure approximate average speed as well. For instance, if you jog a mile in 12 minutes, the tachymeter reading next to 12 will be 300. Divide that by 60 since you're using minutes instead of seconds, and you'll find that you're running an average of 5 miles per hour.

**Tachymeter accuracy**

While a tachymeter is a handy tool to measure approximate times to completion, and approximate number of repetitions per hour, it cannot be absolutely precise. The tachymeter can only use whole seconds in its calculations. Due to space constraints on the dial, measurements are not very precise in actions that take less than eight seconds. Any actions over one minute cannot be measured without doing the calculation on your own, unless it is measured in whole minutes so that the result can be divided by 60. All calculations on the tachymeter assume a constant speed.

**Modern technology versus the tachymeter**

Today, the tachymeter is falling into disuse due to the ever more affordable technology that can be built into watches. If you opt for a digital watch instead of an analog, you probably have a stopwatch that can measure tenths or hundredths of a second. Most digital watches also have a tachymeter display, but it shows the precise measure rather than the closest whole number. In addition, for purposes of measuring speed and distance, it's now possible to buy watches with built-in GPS that will measure your actual change in global positioning. Some watches will even send these times and distances to online tracking services, allowing precise logging of your exercise efforts.

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