This is a hand held instrument that uses air pressure to applanate the cornea. The Pulsair uses a transducer to directly measure the air pressure at the point at which the cornea is flattened. Firing the demo button once will give a value of 30, firing it twice will give a value of 50 if the machine is calibrated. If the readings are higher or lower by the same amount these values can be added or subtracted from the patient’s reading to give accurate results. If the values are not linearly higher or lower than the calibration values, the instrument should not be used prior to being serviced.