I used to, after checking the boiling point of water that day, adjust the zero of the thermometer but at times the density seemed off a little. I then got a Marcland baro/boil temp meter. That helped a lot since by then I had an auto draw. I now check that meter every 2 hours or so, and reset the auto draw if needed. Before that I had only tested the boiling temp to start the day, but the barometric pressure changes often, and with every such change the boiling point of water changes. This might also be part of the issue. I now get very close, but I final check everything using one of my hydrometers. I now use a Smoky Lake Gold hydrometer, it is only better because it has a ref line to indicate if the paper has not moved. When you buy a hydrometer you can make such a mark in the box it came in for future reference. I just never did that in the past.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.