I have been weighing my hives for a while, and I thought that we could share some ideas about that. Last year, I made a portable, simple digital scale that I use to weigh both sides of each hive. The sum of the two measurements is a good approximation of the real weight, as far as the hive's center of mass is near the geometric center of the hive (with which I try to align the sensor). The resolution is 0.1 kg and the maximum error (end of scale - 120 kg) is around 5% due to my poorly designed/built "load cell". BTW, the instrument is a barebone circuit, which should be improved in many features.
Photos are far better than my description: <http://geocities.yahoo.com.br/jbacampos/pesagem.htm> (never mind if the text there is unreadble).
In the apiary, I think the measurements are useful to select which hives I really need to open. The less I disturb the girls, the better it is (for all of us). Of course, the scale doesn't replace manual management, but it helps doing the job in a more rational way. It's amazing how different are the hives' performances in my apiary - a very successful hive in a week can be far from first place in the other. Maybe that's because the bees have a scattered, not very strong nectar sources there, and they probably don't share their findings with the neighbors...
When I enter the data in a spreadsheet, I can also see the total apiary weight and its behavior along the time, and that is a more realistic view of the gathering result. Unfortunately, my last two crops were almost totally ruined by a bad weather, so I couldn't check how strong was the relationship between the total weight and the harvested honey. I too calculate the net weight, trying to find out if I can parse it in (mainly) bees, honey and wax in some way.
I'm still not sure how useful a scale can be, but I'm not letting my lack of imagination rule... [img]smile.gif[/img]
Maybe you have good ideas about that.