Difference Between D/A Trim, Scaled D/A Trim Option in Hart Calibrator

"Scaled D/A Trim:

Scaled D/A Trim is a feature that allows HART® communications users to trim a smart transmitter's 4-20 mA

output using a different analog scale to measure the loop current. For example, an I/O resistor is commonly

placed in series with the two wire 4-20 mA loop to convert the current signal into a voltage signal for use by

the DCS. By measuring the voltage across the I/O resistor, the loop current value can be obtained by

dividing the voltage by the resistor value. Scaled D/A Trim allows the user to enter this voltage directly

instead of having to convert it into the actual current value. During the trim function, the transmitter output is

set to a fixed output (first 4 mA and then 20 mA). The user is prompted to enter the meter reading using the

analog scale selected by the user. The transmitter D/A calibration trim is then adjusted to obtain the correct

meter reading. The resulting calibrated loop delivers a precision voltage signal to the DCS."

http://www.meriam.com/pdf/Manuals/MFT%204000%20400%206.pdf