Used in conjunction with the Razor HD 85mm spotting scope, range work, calling shots and spotter/shooter communication become seamless. It's essentially like having a ruler in your spotting scope -which comes in quite handy. Just like many of Vortex's riflescopes, the eyepiece is available in both MOA and MRAD configurations to match the reticle subtension markings and turret graduations in your riflescope.Note: This eyepiece is specifically designed for use with 85mm Razor HD spotting scopes - it is not compatible with the 65mm and 50mm Razor HD models.