Measuring tapers

[Toolmaker51]

Yes, your self-correction is correct. Only the fact that the blocks have matching dimensions matters. Thanks for remembering my name but that tool is properly called a "dial caliper", not a "vernier". The old style calipers that actually had a vernier scale, might be nicknamed "verniers" but the terminology for the more modern ones is "dial caliper" or "digital caliper" for the purely electronic style.

An important bit of terminology. All three are available, my preference has always been for vernier calipers. I have a 6" digital that I use most often on the lathe getting stock and shoulder lengths near finish size before completing accurate work with a micrometer. I use verniers outside & inside where we haven't a large enough micrometer, or a mic won't get past an obstruction. I have several, from over the years, ranging 6" to 48" and seriously enjoy using them. easy to use, simple to calibrate, and virtually maintenance free - if you preserve the all important storage case. And don't store with a tightened lock screw, or jaws fully closed. Each case has a loose stub of wood dowel between the jaws I've added. If you should bump the case the jaws won't impact each other.

To rasta's description of calipers with different jaw styles. Combined jaws; flat outside, radiused inside faces are typically 'heavy-duty', and also the larger sizes where knife edge jaws prove too delicate. Radiused jaws are a bit more accurate inside too; knife edge have a small, narrow flat on each. The flat is incidental on larger ID's. Smaller ID's might show .001-.003 less than true diameter. The more difficult problem is knife edge don't seek the extreme right and left bore apex of both axis [radial & axial] so readily. That makes consistent measurements iffy, both from a mechanical and tactile standpoint.

In the US, digital calipers are the runaway favorite, last twenty years or so. Only recently have they gotten really nice. Dial calipers have an issue with particles being lodged in the measuring rack, making the pinion jump, and it's uncommon to see one zero out at the twelve o'clock position. They also have two different 'resolutions' which isn't the exact term but affects it. Earlier models read .200 in one complete revolution, with suspect measurements anything less than +/- .004 of true size. Newer .100 dials are good for +/- .002.
Most precision instruments are graded at 4:1 ratio for inspection purposes. That means the instrument must be capable of measuring 1/4 the drawings part tolerance. So + or - .001 = .002 tolerance. The instrument required has to discern .002 / 4 = .0005, a typical micrometer in 1/10th's. Standard micrometers, and indicating micrometers I recall, are the only analog tool that reach into the tenths. Many popular test indicators showing 1/.0005 dials will not reach that repeatability, or repeatedly.
There are differences between what sound alike, in ALL measuring instruments. Accuracy. Resolution. Repeatability.