We used to fill two empty supers nailed to a floor with bricks to the minimum weight we wanted for wintering doubles, take it with us and use it to calibrate our estimations when hefting hives.
We'd just quickly lift the front of each hive a little as we went through the yard and mark any light ones.
We had to heft the benchmark "hive" periodically, though, because after a series of light or heavy hives our mental calibration would be off.
This was surprisingly accurate and we could usually guess weights within a kilo or so.
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