Miguel, some additional thoughts: You should definitely open the instrument and check the controller board A5. First check, if it has the old board, which requires complete exchange of the nvRAMs. On the new version, 66547/66548 with many SMD components, you might change the batteries only. Pictures of the different versions are on Illyas site: https://xdevs.com/fix/hp3458a/#opt002. Otherwise, if you have the old board, and would send 10 years old nvRAMs for calibration, Keysight probably will change this board and charge you for that. (Or you have to tell them explicitly to leave it that way) If you have the old controller board inside, then you might add the 128k memory option for a few bucks by your own. Frank