Get an alcometer they are cheap, I put a hole in the 90 before my condenser for a thermo, now I wish I hadnt! It does sort of tell you what is going on in the run but you cant use it for cuts. I mean when the still gets to 200 degrees your in the tales but you would also see that by the abv% drop with an alcometer. Everything I read said you dont need a thermo in a pot still but I still had to put it in, safety net I guess. BUT your not going to be able to make cuts running 1 gal wash! I would run 5 gal in that, but even there dont expect a large amount of likker after cuts.
Theres more old drunks than there are old Doctors!!