It really varies based on the User i.e. Medical, Trainer, Private Individual, and personal needs.
We offer the Calibration Service to meet the needs of the respective Groups. Medical generally require all equipment to undergo an annual calibration, as they rely very much on the data. Private individuals may also wish to have this service for peace of mind in the knowledge that their device is functioning correctly. However, due to Calibration being a chargeable service, you may choose not to.
Certainly KH2, KH1 products designed for Medical Markets should be calibrated annually.