the best method of Transmitter calibration

Hi friends;
We used rosemount transmitter of diffrent ranges. I want to know what is the best method to calibrate the transmitter. I mean Is it Hart communicator is enough to calibrate it or calibration done by applying a pressure?
Second i want to after how many months to take calibration of smart transmitters?(calibration frequency)
Regards

Pressure VS Hart Communicator?

JCP,

From what I have found, the Hart setup is pretty accurate. But if it were a critical measurement, I think I would want to back it up, with a pressure test. The interval dependent upon the standards, you are trying to maintain.