It's no wonder that the Phoroptor continues to be the industry standard after more than 90 years. Constructed using the finest materials and old-world craftsmanship, every phoroptor has an unmistakable feel of quality. The legendary smoothness and positive detents provide constant reminders that you are using the world's finest refracting instrument. Hundreds of thousands of phoroptors in daily use, and millions of completed refractions, are a testament to the Phoroptor's enduring value. Specifications: Sphere: -19.00D to +16.75D 0.25D Steps +0.12D Sphere in auxiliary dial included Cylinder Power: 0.00D to 6.00D 0.25D Steps Cylinder Axis: 360 degrees (Double 0 to 180 degrees scale) 5 degrees graduations Cross Cylinder: ± 0.25 ± 0.37 or ± 0.05 Optional Prism: 0 to 20 Prism Diopter, 1 Prism Diopter graduations P.D.: 48 mm to 75 mm, 1 mm graduations Vertex Distance: 13.75 mm (normal) Graduations extend range by 6 mm Reading Distance: 5 to 28 inches Auxiliary Dial: 10 lenses plus 2 open apertures *condition of refractor case may vary (minor scratches/defects).