The Rimac bench-mount testers were the standard, maybe still are. Kinda spendy but excellent.
Buddy of mine makes the smaller ones you use in a vise - Jeg's # 80538 is onet - and they also work great, calibrated on his Rimac.
Last I heard, he made them in 300, 600 and 1,000-pound maximums.
Usually $70-$80 depending on the retailer.