Oscillator products are used as frequency/time reference sources, distinguished from crystal products often used for similar purposes by their integration of additional functions for maintenance and stabilization of the resulting output. In minimal form, they consist of a crystal or other resonant element plus functions needed to allow a user to obtain a frequency reference without extensive attention to the operation of the resonant element. More advanced devices integrate temperature compensation or control functions in order to obtain a more stable reference or one capable of selective adjustment.