Sighhhhhhhhh.... Oh here we go again, NICEIC. Bashing!!. Right, what the NICEIC want you to have is a record of basic calibration checks, done monthly, using a ÂŁ20 calcard or home made similar.
That way in the event of your meter going out of calibration a record can be produced for that meter showing its most recent accuracy, other wise if your meter was calibrated 11 1/2 months ago, and it's now showing faulty readings, all of your testing in the last say 11 months can be called into question, and anyone such as HSE, site/ contracts managers can then ask you to go back and re test everything in that 11 month period.
If you can produce monthly records then they may only call in to question the last couple of tests.
This is supposed to be supplementary to annual calibration and my Area eng, describes it as "rectum protectum" seems to make sense to me!