The purpose of the star wheel is to fine tune the location of the gauge needle for accurate readings on the dash gauge.
Turning it CW moves the gauge needle towards the FULL mark. Turning it CCW moves it closer to EMPTY mark. The movement of the star wheel must be done VERY CAREFULLY in just teeny, weeny, itsey, bitsey amounts with a tiny flat blade screwdriver. You must have the patience of a toothache as its a tedious process.
Read all about it in post #4 here.
https://www.fordbarn.com/forum/showt...k+sending+unit