I was going to have to ( as Jeremy Clarkson would say) 'take a brave pill' at some stage to replace the NVRAM that has the calibration data, as it was also very old.
Before I was going to do that I wanted to back up the data.
There are several ways this can be done.
1. Use a Cal Ram Dumper Program that I think was written by Poul-Henning Kamp and modified by Mark Sims (see volt- nuts) "HP3458.exe"
https://www.febo.com/pipermail/volt-nuts/2014-August/003598.html It is contained within the excellent KE5FX program suite
2. TiN has written a program that works with 64 bit Vista Windows, and he also has programs for raspberry Pi / Python program, Linux
https://xdevs.com/article/hp3458a_gpib/#summary. I have almost every version of Windows but Vista 64 and my programming skills are pretty poor so this was
out for me.
3. Take the NVRAM out and read it directly, TiN has done this using the good value and widely available TL866 programmer.
I will do this later.
I went for path 1. initially so if I mucked up I would have something to recover, but using GPIB on a 3458 is a bit tricky I believe as the protocol (488.2) came after the 3458.
My interface was a Prologix GPIB USB interface
http://prologix.biz/gpib-usb-controller.html which I use to interface some of my other gear ( a bit of a HP fan).
I ran into a few problems, the Prologix would only talk to the 3458 if the Prologix powered up disconnected from the 3458 then connected. See 1st photo.
The program of Mark Sims was written for a National Instruments GPIB 232 interface and the command END ALWAYS needs to be sent to the 3458 before hp3458.exe is run otherwise you will get photo 2.
The KE5FX program suite has a GPIB configuration Tool that needs to be in Controller Mode, the GPIB address set and has a command line that will run the HP Basic Commands e.g. ID? and END ALWAYS.