Each error state in the instrument leads to an entry in the error queue.
The entries of the error queue are detailed plain-text error messages
that can be looked at in the ERROR menu via manual control or queried
via the GPIB bus using command "SYSTem:ERRor?".
Each call of "SYSTem:ERRor?" provides one
entry from the error queue. If no error messages are stored there any
more, the instrument responds with 0, "No error".
The error queue should be queried after every SRQ in the controller program as the entries describe the cause of an error more precisely than the status registers. Especially in the test phase of a controller program the error queue should be queried regularly since faulty commands from the controller to the instrument are recorded there as well.