Back when I was using a canner that only had bottom heat, I also watched the level, and heated it to 188-190, shut the flame off and tipped the unit, then I bottled until done, but no real small bottles, usually did qts.
Now with a water jacketed bottler I know, if the syrup temp stayed at a good temp while the thermometer probe was in the syrup, it's still right when the level is below the probe. I now generally start with half gal, then qts, then pints, and I finish with half pints (the smallest side I do). I know how much is left as the thermometer starts to drop because the probe is out of the syrup, the way I have mine set (back sets on a 3/4" thick board, to drain even better, even though the bottom is built with a slight slope). I still have between 7-8 qts, I then decide how many I want in pints and how many should be half pints. I usually finish with a partial half pint, I either take that home or if full enough I give it to one of the grandkids.
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.