When sending a "*IDN?" query to the 8156A optical attenuator over GP-IB why does the instrument return the string "8157A..."?

The 8156A has two command sets for programming over GP-IB. The first is the 8156A command set and the second simulates the command set of a previous optical attenuator, the 8157A. The 8156A will return "8157..." in response to the "*IDN?" if it is set in the 8157A simulation mode.

To select the remote command set for the 8156A use the following steps

1. Press Syst until "COMMANDS" is shown at the bottom of the display.
2. Press Modify to alternate between the "8156SCPI" and "8157SIM" command set. (8156SCPI is the SCPI command set of 8156A; 8157SIM is the 8157 simulation)
3. Cycle the instrument power (switch the instrument off and then back on again) for the chosen command set to become active.