Prism form: Base up,base down,base in,base out Specifications Sphere: 0.0 to -29.50 Diopters, step: 0.25,0. ... : 0.0 to ± 8.75 Diopters,step:0.25 Prism form: Base up,base down,base in,base out Binocular balance: Rotary ... ,±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° Power source: ...