The base frequency of an oscillator is defined as the oscillator frequency prior to any prescaling. Some AVR® devices feature a system clock prescaler. The prescaler register (CLKPR) can be used to scale the system clock with predefined factors. Also, the prescaler can typically be preset through the AVR device fuses. For example, programming the CKDIV8 fuse on devices that offer this option will set up the CLKPR to divide the system clock by eight. This can be done to make sure that the device is operated below a maximum frequency specification. The CLKPR can be modified at run-time to change the frequency of the system clock internally.