Many long years ago when I began my machining apprenticeship - fitting, turning, machining to be exact - I learned to use and love my vernier calipers. They were quicker and more versatile than a micrometer. They could take accurate measurements of insides, outsides and depths to an accuracy of 1-thousandth of an inch - near enough - without any fuss. I still have that old vernier in the garage, unused for nearly 40 years, but you kind of get attached and loyal to things like that.

Time marches on and instruments get refined and redesigned. Although that humble vernier caliper is still a common sight in workshops around the world, there are now two improved versions available; the dial and the digital.

Out of all the measuring instruments ever created for machinists and tool makers, one of the favorites and most useful is the dial caliper.

This precision instrument overcomes one of the setbacks of the original vernier design - the difficulty of viewing and lining up the thin etched lines on the vernier plate and handle by incorporating an easily readable dial. This 360 degree dial and needle is controlled by a high precision rack and pinion system.

Another problem that can occur with the original vernier caliper is a thing called 'parallax error'. This happens when a critical reading is taken from the vernier scale without the eyes of the viewer being in exact alignment with the rulers. This can be overcome with careful focus and by moving the head around - but the dial caliper eliminates that problem completely.

Another useful feature of the dial is the ability to rotate the scale to any point so that a differential measurement can be taken - reading the plus or minus variation from a set size. Also, the caliper slide can be locked in place using a thumb-screw or lever to allow simple 'go or no-go' checks of manufactured parts.

There is no doubt that you can't beat a micrometer when it comes to measuring parts to an accuracy finer than 1000th of an inch - or at those times when plus or minus 1 thou is critical. But to cover a wide range of sizes, you'll need to get your hands on a whole set of expensive mics. The dial caliper on the other hand covers a large range of sizes, and has the bonus of directly taking inside and depth readings. This is what makes it so popular - and usually the first measuring instrument of choice for metal workers.

Caring for this instrument is mostly common sense. They are high-precision, delicate tools so they need to be treated with respect if you want long and accurate service from them. They usually come in their own soft or hard case - and it is a good idea to store them there when not in use. The teeth rack and gear mechanism especially should be kept clear of grime and foreign particles. As with all fine metal tools, a light coating of top-grade instrument oil will keep it operating smooth and rust free.

In the old days, with a young man's eyes, I didn't have many problems with my trusty vernier caliper. But today I'm grateful for the extra clarity and accuracy of that big 'ol needle and fat dial on the modern dial caliper.

Machinist calipers can have a long life when properly cared for. There are many of these used, pre-loved precision instruments for sale on the market today. Take a look at this selection here.

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Calipers come in 3 main variations; Vernier, Dial and Digital (or Electronic.)  An excellent selection of calipers on the market today is produced by the USA company 'Starrett' - makers of a full line of precision tools for machinists and toolmakers etc.