Tektronix 11A32 User's Reference Manual page 21

Operating the 11A32 in 11300-series mainframes
Figure 2-3. Overdrive recovery using long (top) and short (bottom) cables
unterminated. Traces are offset two divisions and the photograph is a double
exposure.
When the input impedance is set to 50 O and the input voltage substantially
exceeds 5 Vrms, the 11A32 will sense the overload, disconnect the 50 Q. input
termination, and connect the 1 MQ termination. The Impedance menu will show
1 MQ, and the mainframe will display the message:
Input channel N overload on LEFT/CENTER/RIGHT plug-In
where N = 1 or 2.
To reset the input impedance to 50 Q, first correct the overload condition, then
select 50 O from the Impedance menu.
11A32 User Reference Supplement 2-7