If it's just a one time curiosity of what is my pull weight, you can throw some spare change in a plastic bag and tie it off to a longer loop of dental floss up and around the trigger. Adjust until you find the weight that can barely lift the bag off the ground without setting off the trigger. Easier if you pull action out of stock but works either way. US quarters are exactly 5 per ounce (0.2 each) or if you have a postal scale you can just grab a handful and adjust as needed.