Really, not a whole lot to this project. I bought a $4 dollar electronic hanging scale from Amazon. This one does not have a MAX memory button so you just have to watch the scale when testing.
All you need to do is take a old plastic hanger that has a metal hook. Take the hook off and straighten it out. Then shape it like in the picture above. The little bend in the hook locks onto the trigger of the gun.
Now remove the original hook from the scale (the one to the right in the picture) and replace it with the one you just made.
P.S. Make sure your firearm is unloaded! Always follow all safety precautions.