Haven't built it yet, but I'm going to. 7000 grs = 1#
Using a similar method jmorris uses, Use a wire bent like Brownell's weigher, but hang a plastic "pan/container" like a large powder scale pan on the bottom hook.
Weigh a number of 125 gr bullets and you'll find that 14=1/4#, 28=1/2#, and 56=1# weights to place in the plastic pan.
The wire and pan would be tare weight measured just one time on a powder scale.
Prepackage enough of the bullet weights shown reasonable for you gun. Add or subtract bullets until the hammer just drops every time. Repeat several times. I would be content with this result.
YMMV
I know 125 gr bullets aren't perfectly accurate weights, but the average weight is VERY close and good enough for most users' trigger measurement interests. One could weigh the bullets that drop the hammer on a scale + the tare weight for more precision.
Wouldn't cost ANYTHING to try using bullets you have on hand, simple to make the wire hanger (see Brownell's pic) and a plastic cup can be made from a plastic Coke bottle or other kitchen trash. Anchor the gun muzzle up in a padded vice or another method. Hang the wire and pan and add the weights . Done
Dang it, I may do it tomorrow.