How do you read a keratometer?

First clean the chin rest and head rest with alcohol. Keep the occluder in up position. Second, turn the eyepiece counter clockwise as far as it can go then turn clockwise until the cross hair is crystal clear (ensuring not to turn the eyepiece back and forth). Next, turn the ON switch on and instruct the patient to place his/her chin on the chin rest and head on the head rest and align the patient. Align the patient based on the location of the leveling pin, lining up the leveling pin with the patient's canthus. Use the elevating knob to assist in locating the mires, once located used the focusing knob to bring the mires into focus (ask patient to blink until the mires are seen) ensuring that the cross hair is placed directly in the middle of the bottom mire to the right. Also focus ensuring the plus signs are on top of each other and the minus signs are aligned, then take the reading. The horizontal drum is read in diopters and assuming the axis is 90 degrees apart, is the reading at 180 degree and the vertical drum is read in diopters at 90 degrees.