ZFMAGFLD overload logic

The overload logic isn't quite right:
- The overload limit is currently `~2250mG` (4.5x range, where range is 500mG/V). As the cDAQ has +/-10V range in reality this can be `4500mG` (9x range) as an overload threshold.
- Logic is currently `field(CALC, "max(A, B, C) > (D * 4.5)")`, this seems to be missing some `ABS()` calls around the measured fields (A, B, C)

Start by locating the ZFMAGFLD overload logic containing `field(CALC, "max(A, B, C) > (D * 4.5)")`. Check the cDAQ +/-10V range and determine the expected threshold and absolute-value handling; done means the overload logic reflects the stated limit and measured-field behavior.

Scritto dal modello di indicizzazione a partire dal testo della issue.