yeah, with a bathroom scale:
string the bow (twist or untwist the string so that it is about 5 inches from the back. )
-get a 2x4 and cut a groove in one end like the nock on an arrow- pad it to protect the string. -consider stapling a piece of sandpaper to the bottom for traction.
-mark numbers on the 2x4 showing inches from the nock.
-next put the 2x4 on the scale, nock end up
-then hold the bow horizontally, rest the string on the nock with the bow hanging down towards the floor.
-next, zero the scale if it's adjustable.
-lastly, pull/push the bow towards the floor like it's being drawn.
post a picture and measurements and we'll tell you how far to draw it. Or for now just stop at the 20 inch mark to be safe. If it pulls 30 lbs at 20 inches , it would pull about 40-50 at 28 inches.
good luck