I'm in NY and since I believe I'm vcompeting with Vermont's reputation, I've always used 66.9 and I do it using a Murphy cup and Smoky Lakes gold hydrometer. That hydrometer has a red line on both the scale inside the stem and another on the glass. As long as those both line up you know it's accurate.
However, if you get any hydrometer tested and it's accurate you can simply record the distance of the red line down in the stem from the very top and recheck that measurement at least once a year plus anytime the hydrometer might get dropped into the test cup. That's generally how a hydrometer gets off, the hydrometer hits the bottom in the hydrometer cup and the paper scale can move ever so slightly, then it happenes a few more times and the paper scale could have moved 1/8th of an inch or more, and it can't even come close to telling you the density of the syrup.
Dave Klish, I recently bought 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.