... base down,base in,base out Specifications Sphere: 0.0 to -29.50 Diopters, step: 0.25,0.50, ... 1,3 0.00 to +26.75 Diopters,step: 0.25,0.50,1 ... ,3 Cylinder: 0.0 to ± 8.75 Diopters,step:0.25 Prism form: Base ... : ±0.25D ,±0.37D ,±0.50D PD: 48 to 80mm in 0.5mm step Retinoscope: +2.00D or+1 ... .50 both sides Corneal alignment: 12 to 20mm by 2mm step and 13.75mm Field of view: 35 ...