I use the lyman electronic as well. The trick is to be able to hold the gun that you are testing as secure as possible. You will also want to center the the pull rod on the center of the trigger. Pull the trigger as slowly as possible to get good three group averages.
I just do it the poor-man's way... Bent wire hook around top of water bottle and hooked on trigger, slowly poor water in bottle until trigger breaks, weigh bottle.
But then again, I only test trigger weight occasionally. I just don't do it enough to justify a $70 gadget.