Digital Calipers are measuring devices used to measure lengths, diameters and depths to considerable accuracy. The illustration below shows the action end of such a typical measuring tool.

Calipers are available in either metal or plastic and vary in the accuracy to which they measure, some cheaper ones measuring to 0.1 mm (0.004″) with the slightly more-expensive ones measuring to 0.01 mm (0.0004″). They are available in either metal, as shown in the above illustration or in plastic or carbon fibre. In general, the metal variety are more stable and therefore, more accurate but in some circumstances, such as when measuring archaeological materials, the softer-jawed, non-metallic versions are preferred.

On some of the very cheap plastic versions, the jaws do not meet exactly, reducing their accuracy.

Calipers come in two varieties, one having an extension at their lower end which may be used for measuring the depth of holes, rims, etc. Such a facility is useful when taking measurements on the types of receiver seen on most trumpets which have a rim at their bottom end. The illustration below shows such a feature on my own calipers.

A reasonable pair of calipers which report to 0.01 mm (0.0004″) may be bought for around 20-25 GBP/dollars/Euros and may be found easily by typing Digital Calipers into your favourite search engine.

A Note for Purists:

I have referred to these instruments as Digital Vernier Calipers and apologise to purists who read this as modern digital calipers have no verniers, they don’t need one as they have the digital readout. However, having been trained using vernier calipers and used them for most of my working life, I like many others, simply added the word digital to the tool when such a facility became available.