The Sweep Ramp is generated in the A12 Synthesizer assembly. The A12 Sweep output is then routed to the A13 Front End Driver Assembly where the sweep voltage is re-routed to the A18 Yig Tuned Oscillator (YTO). A failure of the Span Accuracy test would indicate that the sweep ramp is behaving in a non-linear fashion. If the sweep is non-linear, then the A12 Phase Lock loop may be defective.