a musical instrument accustomed measure small straight distances
a guitar for the accurate measurement of tiny variations of level; esp. for the variations in the level associated with upper areas of two articles of mercury or other substance, or of the identical line at different occuring times. It comprises of a telescopic leveling equipment (d), which slides up or down a perpendicular metallic standard really finely graduated (bb). The telescope is raised or depressed in order to sight the items or areas, and the variations in straight height are therefore shown regarding graduated standard.
a guitar for measuring tiny variations of level between two near things, since, for example, the distance amongst the levels of the mercury in the cistern plus in the tube of a barometer.