Any deviation from a best fit straight line approximation under specified conditions. In regard to YIG-tuned and voltage-controlled oscillators, the maximum output frequency deviation from a best fit straight line approximation of the tuning curve under specified load and constant temperature conditions. In regard to YIG-tuned filters, the maximum deviation (in Mhz) of the measured resonant frequency vs. coil current curve from the ideal linear tuning line over the YIG filter's operating frequency range.