or
Digital Abbe Refractometer DR-M4/1550 nD 1.30000-1.7100 at 589nm Multiple Wavelength 450 589 680 1100 1550nm Min.Scale: nD 0.0001 Measurement Accuracy: nD+/-0.0002 Wavelength Range: 450-1550nm Temp.Range: 5-50C