Waters Autospec Premier Operator's Manual page 51

These are typical starting values for performing dioxin
Rationale:
analysis (the most common type of analysis performed on this
instrument).
Adjust the peak display gain and detector voltage to see the peak
Tip:
top, if necessary.
8. On the Lenses 1 tab, enter 2500 for both Z Focus 2 and Z Focus 3.
Setting these values sometimes saturates the instrument's detector,
Tip:
that is. the peak top becomes flattened. To desaturate the detector,
reduce the value of Detector (V) on the Control 2 tab.
Peak with saturated detector
Having obtained an ion beam, and completed basic tuning of the instrument,
tune using Perflurokerosene (PFK), which has a base peak mass of 69.
Low resolution tuning 2-9