After finding David Riches website on Mathematical Instruments I was inspired to write a piece on the use of workshop measuring tools. However when I looked into this, I discovered that others had already done that for me. Ivan Law's workshop practice series #6 "Measuring and Marking Metals" describes the functionality and use of various measuring tools. He also looks at practical examples of using marking out on castings.
My first purchase was a simple steel ruler followed shortly afterwards by some digital callipers. An alternative would have been vernier callipers but as far as I can tell the only advantage is that they don't use a battery. The digital callipers use so little power that they run from a watch battery which lasts ages, over 3 years intermittent use in my case.
Verniers are used on other items such as depth and surface gauges but again given the convenience and price digital gauges are taking over from them.
I've also purchased some cheap inside and outside callipers which can be used for transferring measurements between your ruler or drawings and your workpiece. These don't work well for me as when they are totally closed the tips don't properly align which makes measuring small items difficult. I think I should spend a bit more on some better made smaller callipers.
One tool that I don't currently have in my workshop is a micrometer. Typically these are though of as being more accurate than a calliper but at the moment I don't have anything that might need such accuracy. Anything that needs a close fit I'll take the old school approach of machining it based on the mating component as I don't make things that are interchangable.
I must also mention "how round is your circle" a great book by John Bryant and Chris Sangwin. This has a great section on verniers and how they work, it also has a whole chapter dedicated to "Building the worlds first ruler".
Thanks to David M Riches for the photographs of old instruments.
Andy Buffler - Using a Vernier Calliper
David M Riches - Maths Instruments
The Scientific Instrument Society
How Round Is Your Circle
Mikes Models - Digital Callipers vs Micrometer
Models from the cupboard: Class 20
2 hours ago