In production the internal RC oscillator is calibrated at a specific supply voltage, typically 5V or 3.3V. Refer to the datasheet of the individual device for information about the operating voltage used during calibration. The accuracy of the factory calibration is typically within ±3% or ±10%, depending on the device (refer to the datasheet). If a design needs accuracy beyond what can be offered by the standard factory calibration, it is possible to perform a secondary calibration of the RC oscillator. By doing this it is possible to obtain a frequency accuracy typically within ±1% (±2% for devices that have a ±10% accuracy from factory calibration). It is also possible to shift the frequency of the oscillator as part of the user calibration procedure.