I'll throw my 2 cents in; I use calipers very often for many things
when I turn pens and consider them to be an important tool.
Wouldn't want to be without them, as a matter of fact!
I don't use them to measure blanks as I turn,
but I do use them for measuring:
*tubes, inside and out, and length.
* bushings, to make sure they are the right order, and match kit
properly.
*Kit fittings, to verify they are what size you just picked the bushing for.
*drill bits, there are times when you want to know exactly what size it is.
* length of finished blanks, or trimmed blanks, to see if you made it too short
for the parts to work right.
* measuring all the small things in your shop that you never knew just what size they were. For example; segmenting..what size kerf blade have you got. what size strip
for that kerf did you just saw.
handy for measuring bolts, screws, dowel rods, pins,etc.
I have at least two pairs at any time in the shop.Reason being, about once a year
I drop one and ruin it.Need another to carry on until replaced.
I also have micrometers, but that is more metalworking related.
A good dial/digital caliper is usually good for +/- .001 accuracy, check the mfg. specs on this.
AVOID the plastic framed calipers like the plague, accuracy varies, but average
is +/- .005-.015 range.a waste of good money in my opinion.
Also, for anyone's calipers out there, if they have not been calibrated and verified to be accurate still, don't bet that they are. A drop in the floor or good flip
on the workbench can work ruin.Also, keeping the little teeth clean, or sliding area
can be a factor in accuracy.Burrs on the jaws are a killer.Dropped hard, and a burr is very likely to occur. Burrs can be gently stoned off, but it is
a delicate thing.
Just my thoughts!