HP 68302 User Manual page 524

Safety Symbols Used In Manuals
The following is a list of general definitions of safety symbols used on
equipment or in manuals:
Instruction manual symbol: the product is marked with this symbol when it is
necessary for the user to refer to the instruction manual in order to protect
against damage to the instrument.
Indicates dangerous voltage (terminals fed from the interior by voltage
exceeding 1000 volts must be marked with this symbol).
Protective conductor terminal. For protection against electrical shock in case
of a fault. Used with field wiring terminals to indicate the terminal which
must be connected to ground before operating the equipment.
Low-noise or noiseless, clean ground (earth) terminal. Used for a signal
common, as well as providing protection against electrical shock in case of a
fault. A terminal marked with this symbol must be connected to ground in the
manner described in the installation (operating) manual before operating the
equipment.
Frame or chassis terminal. A connection to the frame (chassis) of the
equipment which normally includes all exposed metal structures.
Alternating current (power line).
Direct current (power line).
Alternating or direct current (power line).