屈光度
Diopter \Di*op"ter\, Dioptra \Di*op"tra\, n. [L. dioptra, fr.
Gr. ?. See 2d {Dioptric}.]
An optical instrument, invented by Hipparchus, for taking
altitudes, leveling, etc.
diopter
n : a unit of measurement of the refractive power of a lens
which is equal to the reciprocal of the focal length
measured in meters