HP 8920B Programmer's Manual page 646

Negative Numbered Error Messages
646
Negative numbers preceding the error messages text correspond to the error conditions
outlined in the Standard Commands for Programmable Instruments (SCPI). For more
information on SCPI, order the following book,
A Beginner's Guide to SCPI Addison-Wesley Publishing Company ISBN 0-201-56350-9
HP P/N 5010-7166
or contact,
Fred Bode, Executive Director SCPI Consortium
8380 Hercules Drive, Suite P3
La Mesa, CA 91942
Phone: (619) 697-8790, FAX: (619) 697-5955 CompuServe Number: 76516,254
Negative numbered error messages take the form: ERROR -XX <error message>
For example
Error -128 Numeric data not allowed
or
Error -141 Invalid character data