I heard if you checked your meter regulary and kept a record then it was 3 yrs but MY meter was part of a course i did 18 months ago and has manufacturers cert I contacted megger to ask them does it need re calibratation as i havnt used it from date of purchase the cert is now over 18 months old when i cantacted negger they said the calobration cert only begins date fo first commision and you fill in the relevent box on the cert with date of first use I contacted Elecsa they said that would be fine this was about a month ago I rang again last week to check before registering to ask a few things so asked again to be sure and this time tech guy said that the cert had to be no more than 1 year old but dont worry this would just result in a non conformancy then i would have to get it calibrated again and send evidence to prove its done to gain a pass for the assesment ????So best thing to do is get it done seems to me no one knows depends on who you ask lol