Not wanting to pay the prices asked for "proper" trigger pull gauges, I bought one of these...
Checked against known accurate weights it was 10g low at 500g but spot on at 1kg 1.5kg and 2kg.
A wire coat hanger supplied the necessary link to the trigger and job done.
Other scales are available. I would suggest getting one with as low an upper limit as possible.
You'll be looking at using the bottom end of the range and a wide range means more innacurate at the bottom.