The Collaborative International Dictionary
Dynameter \Dy*nam"e*ter\, n. [Gr. ? power + -meter: cf. F. dynam[`e]tre. Cf. Dynamometer.]
A dynamometer.
(Opt.) An instrument for determining the magnifying power of telescopes, consisting usually of a doubleimage micrometer applied to the eye end of a telescope for measuring accurately the diameter of the image of the object glass there formed; which measurement, compared with the actual diameter of the glass, gives the magnifying power.
Wiktionary
n. An instrument used to measure the magnification of a telescope.
Wikipedia
A dynameter is an instrument that measures the magnification of a telescope. It is usually a double-image micrometer used to measure the diameter of the image of the object glass. The magnifying power is found by comparing the actual diameter of the glass with the measured diameter of the image of the glass .