So I've bought a few used endmills off ebay (I have a habit of snapping them, which hurts when you pay new) ...bit of a lucky dip of 15 end mills/drills.

So how do I establish the true diameter of these - I have digital calipers, but even those end mills I already own & I know the cutting diameter, they measure under - eg 2.00m diameter end mills on my digitial calipers read about 1.86mm (or thereabouts), is it just a case of rounding up?