variometer

noun

var·​i·​om·​e·​ter ˌver-ē-ˈä-mə-tər 

1

: an instrument for measuring magnetic declination

2

: an aeronautical instrument for indicating rate of climb

Word History

Etymology

borrowed from German Variometer, from vario- vario- + -meter -meter

First Known Use

circa 1889, in the meaning defined at sense 1