The normal certification interval X-Rite recommends is 12 months. New instruments still get 18 months from the date of manufacture to allow for delays in the distribution channel.
As a company, we are ISO 9001 registered. Some of our color & appearance products comply with the more stringent ISO 17025 that applies to calibration labs (see our on-line certificate for the instruments covered). One of the requirements of ISO 17025 is that the calibration interval be set by the customer not the manufacturer or the calibration lab. We do provide a general recommendation of annual certification, but each customer has to decide whether his conditions are average or not.
Customers must consider the potential consequences and costs of incorrect measurements. If a non-conforming instrument is easily detected in the workflow or the cost of incorrect measurements is minimal, a customer may rightfully decide to not send in the instrument until he gets an error message.
Obviously, nobody can guarantee that the instrument will perform perfectly within any given certification period. Conscientious customers will have regular checks in place that verify the proper performance of their instrument. The calibration and recertification services that X-Rite's authorized repair centers provide guarantee that the instrument is in compliance with the manufacturer's current specifications. These certifications renew the instrument's traceability to national standards. They also minimize future problems by analyzing components and recommending parts replacement where necessary.
As far as the accuracy and repeatability specifications are concerned, we do not expect an instrument to be out of specification after 12 or even 18 months. But, obviously, due to the varied environments and intensity of usage, there is a potential that some instruments may be out of our specifications as their lamps or electronics may deteriorate.