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This is a Veritas measuring device. It was used to measure the size of Bullers rings. The system was set up so that an unfired ring would measure close to zero (the difference from zero was added or subtracted from the final measure). These rings provided a measure of what temperature the kiln was (as opposed to cones which say what it is). Actually, many companies placed many rings in a firing and extracted them, one-at-a-time (using a metal rod), cooled them quickly and measured them; this gave an accurate indication of the current temperature. Some companies still use these today to verify electronic measuring devices. The Orton TempCHEK system is based on this same principles, but is much more refined (and much more accurate).