Refractive index or Abbe number (?d or ?e) can be measured at different wavelengths ranging from 450 to 1,100nm.The DR-M2 digitally displays measurement result of refractive index or Abbe number on the LCD. Measurement can be achieved by matching the boundary line with the intersection point of the cross hairs. This refractometer is connectable with Digital printer DP-AD(B) (Optional).