>>> My 732A<x-apple-data-detectors://28> e.g. has a drift of only about 0.2ppm pa over a couple of year Hope you don't mind me jumping on this thread and asking a basic question: is there any kind of procedure for the 'enthusiast' (say with single 3458A/single 732 and not say 4x732) to measure the drift of a particular 732. Alan