According written recommendation from Gossen Metrawatt (one of older European analog multimeter maker ), analog meter calibration interval this varying according operating condition's of the instrument.
In detail :
The respective measuring task and the stress to which your measuring instrument is subjected affect the ageing of the components and may result in deviations from the guaranteed accuracy.
If high measuring accuracy is required and the instrument is frequently used in field applications, combined with transport stress and great temperature fluctuations, we recommend a relatively short calibration interval of 1 year.
If your measuring instrument is mainly used in the laboratory and indoors without being exposed to any major climatic or mechanical stress, a calibration interval of 2-3 years is usually sufficient.
Verification of specifications or adjustment services are not part of the calibration.