All instruments lose accuracy over time due to normal usage and the environmental conditions to which they are exposed. Periodic NIST certified calibrations maintain the accuracy of your data loggers and chart recorders throughout their lives.
Periodic calibrations that include both before and after calibration data are the ONLY way to ensure that measuring instruments are accurate and can identify out-of-tolerance conditions.
A wide range of regulations-- GMP, FDA, HAACP, USDA, ISO 9000 and ISO 14000, JCAHO, CDC, EPA, among others--require strict adherence to regular calibration schedules and documentation of data logger and chart recorder measurement accuracy.
Standard operating procedures that demonstrate due diligence in adhering to calibration schedules and documented proof (including both before and after calibration data) protect from liability claims.