Glass tube of about 6mm bore is encased in an enameled and lacquered brass tube, mounted on a polished wooden board with provision for wall mounting. With chemically engraved, silvered scales, graduated in both mm and 1/10” accompanied with a Vernier having a least count of 0.1mm or 1/200 inch of mercury that moves with rack and pinion arrangement and is mounted between the two scales, complete arrangement enclosed in a glass cylinder.