A Glowgem Testometer is a device that measures the strength and "flavor" of a glowgem. The device is powered by the glowgem itself. A glowgem's strength corresponds to the amount of lit bars. Only strength is reliably measured.
Flavors are more unreliable. The inscription on the bars from left to right: Dada, Sukkot, Rehab, Yonder, Water, Greet.
They were invented by Griffington.