Shows where the protective ground terminal is connected inside the instrument. Never remove or loosen this screw
This symbol is used for identifying the functional ground of an I/O signal. It is always connected to the instrument chassis.
Indicates that the operator should consult the manual.
One such symbol is printed on the instrument, below the A and B inputs. It points out that the damage level for the input voltage decreases from 350 Vp to 12Vrms when you switch the input impedance from 1 MΩ to 50 Ω.