Hello, I just want to give notice, that I also have replaced successfully those 3 NVRAMs in my HP3458A from 2000. The cal data had been saved by the MREAD command (thank you again, Poul-Henning). Both 32k*8 and the CalRam DS1220Y with date code 9935 were still alive, but it was not possible to measure the internal battery voltage over the protection diode reverse current. A fellow volt-nut (not active here on this list) programmed the fresh DS1220AD for me. He owns an HP3458A from 1989, which had 2 exhausted 32k*8 DS1235Y, but the Cal Ram, DC 8840 (!) was still ok. In 2009, I had lowered the LTZ1000A temperature in my 3458A to about 55°C, for a quasi opt. 02. The long term monitoring of the 3458A against a Fluke 5442A and two other LTZ1000 references (@ 7,147V, running 24/7) still shows, that the whole group of 4 references agree within +/-1.5ppm after that 4 years period. The recent comparison to the (obviously freshly calibrated) gear of my fellow volt-nut agreed within < 1ppm. So, my 3458A (opt. 01+02) should be healthy for the next 15 years. Frank