Periodic calibration of a data logger increases measurement confidence by comparing a measurement device to a traceable standard. Proper periodic calibration ensures the accuracy of a data logger throughout its life.
All physical sensors become less accurate due to the environment, usage, stress, and even time. The degree to which these changes occur varies from device to device. For example, a voltage device will drift very little over the years whereas a humidity sensor can drift significantly in several weeks if subjected to a corrosive environment.