Wayne
per manual pg 14-19. Btw this is an optional guage and is not part of the mel.
1) make sure front adjument screws are in mid position. Adjustment bars are in mid position
2) partially remove instrument and test fly.
3) set power to 75% and lean for peak egt. Adjust rear screws so instrument reads 4/5 full scale. Both should read the same.
4) reinstall. The instrument will drift a little after use and the front screws can be used to readjust in (3).
Probably you tried to peak at less than 75% power and the egt is not hot enough to get to the 4/5 th's of full scale.
on the P337 the say to enrich to +50 degrees and should require 9 +/- 3 pph on the fuel flow guages.
The pointers should agree to within 1/2 increment of each others at PEAK EGT. again 75% PWR.
BTW your tack issue. There are some very accurate hand held tacks for less than 150 dollars that can be used inside the cockpit to keep accurate. The alternative is the small JPI tack that uses the P lead and install on one engine. You then need not worry too much about calibration of the very inaccurate, sloppy, bouncy, crappy tacks on the aircraft.........
bet this will help
Bob