20D measurement, AC and DC power High quality CE, external reading Range of vertex diopter measurement: From 0D to ± 20D step: 0.12D Range of prismatic diopter measurement: 5 prism diopter step: 1 diopter Range of Cylinder axis: 0 ~180 degree step: 1degree Accepted lens diameter: 20mm~85mm Eyepiece focusing: -5D~+5D Power supply: AC 110V or 220V, DC 3V