1... After you have ground balanced, do it again about 15 to 20 minutes later when the coil temperature and electronics have matched the air temps... 2...The ground balance at the bottom of hills may be different at the bottom as opposed to the top due to the possibility of more moisture at the bottom . A note about Tesoro coils. I've owned just about every one. In switching coils, and GBing with a 10 turn pot (over a special area), none have been "off" by more than a half turn.. A bit of rain, a carving project to finish...If all goes well , will turn the Vaquero loose after Supper in a last ditch attempt to find another keeper at the mansion.