Transmitters are calibrated by hooking up a Hart transmitter,collect as found reading 2. Check for zero error by venting/draining the sensing line to the transmitter ( note.. transmitter must be isolated before venting/draining) 3. Zero trim if there is zero error 4. Perform multi point calibration using a pressure source in an ascending and descending order of 0,25,50,75 and 100% 5. After calibration pass,return transmitter to service