A Graduated Chamber Gauge is Absolutely & Totally Dependant on an exact match of diameters with chamber end. Their use was promoted & advertised by sellers of Chamber Reamers, or Gunsmiths doing chamber jobs. Many, Many a chamber has been reamed & tampered with because it just happened to be a thou or two under-size which was totally immaterial, but they brought a few entrepreneurs a bundle of Cash. Having checked a few chambers short which were not I discontinued use of a "Chamber Gauge" & depend on my Starrett 6" scale, measuring to the shadow line. A $3.00 General scale from your home improvement store will do the same job just as well, I just happen to still have my Starrett. "IF" the gauge is not an exact match to the chamber diameter the scale is the more accurate.
Those internal dial calipers as pictured are very good, but expensive unless one has a lot of use for them. I don't need one that often. Such items were company furnished at work so I didn't have one in my personally owned toolbox.
PS; Many of those chambers I mentioned were "Fixed" because of a chamber gauge, "BUT" they "Weren't Broke".
