No. There is no rule demanding that measuring instruments must be calibrated once a year, unless stipulated otherwise in the regulations. It is up to the user to determine the interval between calibrations. Certain usages may require an instrument to be calibrated several times a year, or only once every 10 years. The only requirement that is frequently found in the reference standards is that the rules must be drawn up in order to determine the interval between calibrations. The Afnor document FDX07-014 "Optimisation des intervalles de confirmation métrologique des équipements de mesure" (Optimisation of the intervals between metrological confirmations of measuring equipment) describes a number of methods to determine these intervals.