from
The Collaborative International Dictionary of English v.0.48
Cathetometer \Cath`e*tom"e*ter\, n. [From Gr. ? vertical height
+ -meter.]
An instrument for the accurate measurement of small
differences of height; esp. of the differences in the height
of the upper surfaces of two columns of mercury or other
fluid, or of the same column at different times. It consists
of a telescopic leveling apparatus (d), which slides up or
down a perpendicular metallic standard very finely graduated
(bb). The telescope is raised or depressed in order to sight
the objects or surfaces, and the differences in vertical
height are thus shown on the graduated standard. [Written
also {kathetometer}.]
[1913 Webster]