Tools - Vernier Callipers

This description is not copied from a book and is therefore in my own words, so some of the terms/names may be wrong, but the method is correct. I work in millimetres as I was brought up and educated with the metric system. However some plastic section is sold in thou (thousandths of an inch) as well as Scalextric axles which are 3/32 inch.

Look where the zero on the Other Scale meets the Main Scale. The figure to the left on the Main Scale gives you the whole millimetres. e.g. here 3mm. Then you look which line on the Other Scale 'lines up' with a line on the Main Scale. There should only be one except when 0 and 10 both line up. This gives the decimal part. E.g. The line marked 4 on the Other Scale lines up with a line on the Main Scale (7 but this is not important). This means the measurement is 3.4mm.

When working with plasticard I can only work to + 0.25mm which is less accurate than the callipers so why use them? With its parallel jaws I find them very easy to use, even if I round the measured value to the nearest 0.5mm afterwards.