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To make it useful, it needs is a set of weights like these:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220419469395
Lock the balance with the desired number of grams (grains) from the weight set, and you're good to go.
GOOD GOSH!
Those weights are set in GRAMS, not grains. You'll get yourself killed for sure with those.
Reloading is always done in grains.
None of the ideas are valid for how to use this scale for reloading.
To use it, you would have to measure something out on a known scale, and transfer the material weighed to the old scale, and set the adjustment to point to zero. In which case, what would be the purpose since you already have a scale to do that.
What would be neat to check out, however is if the old scale has some kind of a notch or mark on that rotating nut. If it does, it could be that every rotation of the nut is some fixed amount, like 1 grain, or tenth of a grain. You'd have to check it to find out. If it is calibrated in that manner, it would still be a pain to work with since it would require keeping track of how many revolutions you made with the nut. More work and effort than it's worth.
My advice is to keep it OUT of the reloading circuit.
Now that I have been looking at the picture again, it looks like it's actually a bit LARGE??? Is it?
If so, it could be set for measuring things in OUNCES.
So, in a General Store at the turn of the previous century (1900), you could use it to sell an ounce of tobacco, or a pound of flour... that sort of thing.