The PD Meter is a digital precision optical instrument used to measure distance between human pupils in the process of optometry for fitting spectacles. Detailed Product Description: 1, It employs precise optical structure, the line of light is very clear and precise measurement.The measurement results are displayed digitally,and the left eye and right eye measuring values are displayed separately. 2, Simple and rapid measuring operation, and free operation of the direct PD adjustment lever are possible.Combining with the adjustable viewing distance selecting lever for measuring all kind of the viewing distances, the PD measurement is simple and precise. 3, When the measuring operation is finished, the auto poweroff and memory function,enable to save the power and not to lose the data. 4, It can also be used in monocular the left eye and right eye separately. Parameter: Effective range of measurement: binocular pupillary distance:45-80mm， left or right pupillary distance:22.5-40mm， Indication error: ≤0.5mm Distance of targent: 30cm ～ ∞ Electric Voltage：DC 4.5V(3pcs 5# AA battery) Power：10W Weight：0.6kg Volume：21.5(L)x15(w)x50(H)cm