It is a free optical calculator tool for opticians, optometrists and ophthalmologists and lab technicians. Use it to do all your diopter to radius conversions. Calculate lens power at different vertex distances. Calculate manifest over refraction even with cross cylinders. Use it to calculate contact lens power and toric lenses as well. Calculate lens transposition at any time. No need for diopter conversion tables or charts. No need for radius conversion tables or charts. No need for formulas or equations to remember.