tachograph vs tachometer

tachograph and tachometer both are nouns.

Word	Noun	Adjective	Verb	Adverb
tachograph	Yes	No	No	No
tachometer	Yes	No	No	No

As nouns, tachometer is a hypernym of tachograph; that is, tachometer is a word with a broader meaning than tachograph:

tachograph: a tachometer that produces a graphical record of its readings; used to record the speed and duration of trips in a motor vehicle
tachometer: measuring instrument for indicating speed of rotation

Other hypernyms of tachograph include tach.

tachograph (noun)	tachometer (noun)
a tachometer that produces a graphical record of its readings; used to record the speed and duration of trips in a motor vehicle	measuring instrument for indicating speed of rotation