Chad, as a physician, I know that kidney stone pain is some of the worse pain anyone can experience! Hoping all goes well tomorrow and that you get major relief of your pain, and that your 6 mm stone becomes ancient history!
Most calipers will do both. Mine has a small button to push for either mm or inches. A 0.625 inch marble normally would be reported as a 5/8” marble. However, it is not a really big deal, although some threads in the past have denoted that fractions are highly preferred.
I can see Carlos Santana but not Jimmy Hendrix! Seriously, the first looks like a modern confetti marble, the second one a Vitro helmet and the last a Master sunburst IMHO.
Well, not exactly the same after further inspection. If you’re interested, most antique booths will take 10% off if you ask. Seems about right price wise compared to other ones I’ve seen.