Tool Trucks all have a simple checker --they will check for free and they are close enough--the way you use the wrench has more impact on correct tq than the wrench--never jerk it like you see the NHRA guys doing on a million dollar funny car--one smooth pull---last batch I had I checked four from my shop--cheapos--Snap Ons, Etc all were near enough--it is surprising how close they all were when you look at price and the Snap On 3/8ths is the one that is always breaking a tooth in the head--once a year easy--others never any problem--FWIW the one from Lowes for $50 was dead on enough for the space shuttle