HP 70427A User Manual page 606

Figure 15-5 Frequency Adjustment Access
4. Remove cover.
5. Remove the adjustment cover screw on top of A5Y1 to allow access to
frequency adjustment.
6. Adjust A5Y1 with a (non-metallic adjustment tool) so that the signal on
"Input A" of the oscilloscope moves less than one cycle in 10 seconds.
10 MHz Oscillator Adjustment
HP 70427A/HP 70428A User's Guide 15-9
Adjustments