Hello Time-Nuts, Pete Lancashire was wondering how many HP 5065As are out there. I don't know the exact number, but I know there are a lot. I think Corby (or someone) had a list of serial numbers at one time. I will confess that I do have one - and love it. It is a very old unit that doesn't have any updates other than a few new electrolytics and a finer adjustment on the C-field. Attached is a plot of it for the last three days. I have not touched it in several months. It is not in a particularly well controlled temperature environment (the yellow line on the graph), and it moved 110ns in three days (4.23x10E-13 frequency error). And most of the noise on the purple line (5065A frequency) is due to the GPS reference (NTBW50AA does not have a great antenna as indicated by the bottom GPS line). Skip Withrow