If you haven't seen it yet this link is the latest update regaurding scales

http://www.dh.gov.uk/en/Publicationsandstatistics/Lettersandcirculars/Estatesalerts/DH_114046

We have had trading standards in twice checking our scales and they really go to town i.e. weights on all four corners then total weight allowance over entire scale surface. Path lab scales were tested down to milligrams and if anything was out of cal the scales were withdrawn from service by trading standards. All class 3 scales can only be calibrated / repaired by the manufactures unless you have all the correct equipment / certification / up to date paper work and able to employ somebody to look after all of this, good luck.