On the kit the Pot should look the same as the one that was in there for the 550 meter, if not I wonder if it is the wrong one as those I got for the kits I sell look the same. They mount the same too so you just got to desolder the one that is in there and put the new one in and re solder it again as it only goes in so far into the circuit board. On the numbers that is shown I am not sure the range that is shown before the course calibration control is set, but I believe after it is done correctly the range I believe is around 170-183, but not 100% sure. There has to be enough to adjust it to 180 for which ever coil you use and any change in the temp change. The resistors are 1% tolerance where most are 10% so they are very important to use the right ones. Another thing is the soldering of it as you use a solder pencil not a gun and do not use acid core solder or flux solder as it will ruin the circuit board. check your solder on the circuit board so you do have a good connection and no solder bridges across 2 points where it should not be.
The meter is really a voltage meter and runs off the tones of the Sovereign, so if the numbers are jumpy the tones should be too and why I will set the sensitivity to auto so it is easier to set up the calibration. The meter and tones will read what the coil is seeing, so if you have any interference it will show up on the numbers on the meter which can cause the numbers to be erratic. The best way is waving the coin by the coil not real slow and not real fast, but doing this I try to keep the tone as steady and smooth as I can and watch for the highest number as that will be what you are trying to get 180 on, if it goes 180 and bounces to 179 that is OK too.
Good Luck and keep us informed.
Rick