All Bar Weights are calibrated here at JWS to the specification listed below:

M1 is the most accurate at +/-250mg.
M3 is +/-2500mg

If you want the test weight independently verified select 'Trading Standards Stamped'. Remember to add a Trading Standards Certificate to your basket available back on the Bar Weights page where you can also purchase a UKAS Certificate and JWS Certificate of Conformity. 

These weights can have stenciled or stamped serial numbers put on them. Contact us for more details.

Only one Certificate is needed per batch of weights on the same order.