Stanford Research Systems SR810 Manual page 62

Front Panel
[Auto Offset]
[Expand]
Reference Display to its original display, press the desired reference
display key ([Phase], [Freq], [Ampl], [Harm #] or [Aux Out]).
Pressing this key automatically sets the X or R offset percentage to
offset the selected output quantity to zero.
Pressing this key selects the X and R Expand. Use the [Display] key to
select either X or R. The expand can be 1 (no expand), 10 or 100. If the
expand is 10 or 100, the Expand indicator below the display will turn on.
The output can never exceed full scale when expanded. For example, if
an output is 10 % of full scale, the largest expand (with no offset) which
does not overload is 10. An output expanded beyond full scale will be
overloaded.
Short Time Constant Limitations
A short time constant places a limit on the total amount of DC gain
(reserve plus expand) available. If the time constant is short, the filter
slope low and the dynamic reserve high, then increasing the expand may
change the time constant. See the table of time constants and DC gains
in the Gain and Time Constant section.
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