Old Pierre Vernier watched the last episode of Game of Thrones and now he's bored. Disappointed, oddly empty feeling, and did I mention bored? Even though he was the Castellan of a real friggin’ castle, he had time on his hands. Pierre was not a seafarin’ fella, but he knew all dubloons were coming in because of globalization. We’ll skip his views on Milton Friedman, sufficed to say he wrote a brief pamphlet on the subject called Commerciaque non liberum. Pamphlets were the Tiktok of the late 1500’s. Pierre set out to improve the quadrant, which was the "Siri where is the nearest Dunkin Donuts?" of the time. To do so, he added the Vernier scale (which he originally called the ‘Pierre is so damn smart’ scale) at the bottom of calipers. This scale introduces hyper acuity, i.e. the ability to see things beyond what the naked eye can see. Put some clothes on, eye!
Here’s how it works, courtesy and without permission of Wikipedia:
Vernier caliper scales; main at top, vernier at bottom. It reads 3.58 mm ± 0.02 mm by adding 3.00 mm (left red mark) on the fixed main scale to vernier 0.58 mm (right red mark). The main scale reading is the rightmost graduation that is to the left of the zero on the vernier scale. The vernier reading is found by locating the best aligned lines between the two scales. The 0.02 mm engraving indicates the caliper's accuracy and is the "Vernier constant" for this scale."
Everyone that works on bikes, even casually, should have a Vernier Caliper. There are really cheap ones out there (I tried to find a cheaper one to sell, and none of them passed basic muster, so we’re going with a decent one) but you only have to buy it once, they don’t wear out. This Unior one is essentially indestructible. Dial Calipers don’t like falling down, and digital calipers need batteries, which always seem to be dead. Get a simple analog caliper, like this Unior Vernier Caliper and call it a day.
Things you can use it for:
Measuring seat tubes and seat post sizes. Bolt thread pitches. Bolt diameters. Bar diameters, steerer diameters, headset sizes, crown race sizes, bottom bracket shell widths, Bottom bracket spindle widths, pedal threads, brake reach, drop out spacing, jockey wheel to cassette spacing, chain wear, bolt circle diameters and probably stuff I am not thinking about right now. In short, it’s more useful than a ruler for bike work.
The Unior caliper is good, solid, tough, reliable. A fine workhorse caliper that will last 50 years easily.