Marking GAUGE CALIPER

[mklotz]

For scales divided into sensible decimal values, designing a vernier isn't very difficult.

Decide the smallest interval on the main scale you wish to further subdivide using the vernier. As an example we'll use the vernier designed in the OP so this value is 1 mm.

Decide the approximate length you wish the vernier to span; this value affects how easily it can be read. In the OP the approximate length of the vernier scale is 40 mm.

Subtract the first value from the second... 40 - 1 = 39 mm

Divide that length into ten units. Thus each interval on the vernier is 39 / 10 = 3.9 mm. Examination of the photographs in the OP shows this to be correct.

A further example... If the vernier were chosen to span a more conventional 10 mm then 10 - 1 = 9 and the vernier would have ten divisions, each 0.9 mm long for a span of 9 mm, or about a centimeter (0.4") which might be hard for old guys with less than perfect vision to read.

If your ruler is one of those wacky inferial ones graduated in fractions, the same approach I outlined above can be used, though the ensuing confusion it will provoke is another kick in the a.. to adopt metric.

There is a free program, LVERN, on my page for designing linear verniers but it's not one of my best efforts. It's mathematically correct but the user interface isn't something of which I'm proud.