The next time you get into your car, take a moment and look at the dashboard display. Regardless of what ancillary functions you might find, you will definitely find the basics: speedometer, fuel gauge, engine temperature, and the RPM measure. The first 2 make obvious sense – especially if you’ve ever run out of petrol or been fined for speeding. While keeping your engine from overheating makes sense, the RPM measure is a bit of a mystery. Rest assured, that measure is important, but it’s also today’s word.
Measuring revolutions per minute, the correct name for the gauge on our dashboard is a tachometer. Coming from the combination of the Latinized form of Greek takho-, derived from takhos and meaning ‘speed or velocity’, and -meter, which comes from the Greek metron and means a ‘device or instrument for measuring’, our word is literally and figuratively a device that measures speed.
First used in the Transactions of the Society, Instituted at London, for the Encouragement of Arts, Manufactures, and Commerce (later to become the RSA Journal), when Bryan Donkin – the man who coined the term – wrote in 1810: “An instrument of my invention for indicating the velocity of machines, and which may not improperly be called a Tachometer.”
It’s worth noting that, though the term measures speed, in the case of engines like you would find in automobiles or aircraft, it’s important not to confuse its function with the speedometer. While the speedometer measures the speed of movement of the vehicle, the tachometer measures the speed of the revolutions per minute of the engine’s crankshaft, which actually (a few steps down the line) is what puts the vehicle into motion.
With its first usage relative to aircraft found in the United States Naval Consulting Board’s Bulletin No. 3. 10 of 1918, which states that: “Many new instruments have been devised for aircraft. These include..tachometers, which indicate the engine speed”, it’s easy to assume that the term has always been associated with engines. As with many words, however, it wasn’t long until the word became generalized as simply a measure of speed, which can be found in the 1864 edition of Webster’s American Dictionary of the English Language, defined as: “an instrument for measuring the velocity of running water in rivers, canals, &c.”
Still, we most often use this term in relation with moving machines, aka transportation. Moreover, at a time when we concern ourselves with things like WiFi, Bluetooth connectivity, heated seats with a massage function, and even cup holders, we gloss over the fact that, without a properly-functioning tachometer to gauge engine function, we might be forced into sitting in a stationary composite/metal box staring at that dreaded “Check Engine” light on the dashboard.