I have a spare REV A Ref Board, 03458-66509, from a 3458A. I need to know if the LTZ1000 reference IC is a 1000 or a 1000A chip, as they have different temp set points and thermal losses. The LTZ1000 on my board only has the HP part number, 1826-1860. I have an HP X-ref, but this number is not listed. If anyone knows for sure which version of the LTZ1000 this is, it will help many besides myself. Best, Dick Moore