I will be the first to admit that I don't have an intuitive feel for network analyzers, so I would like someone to explain this to me: I am checking out an 8753E to purchase, and after it passes its power-on self-test, and with nothing hooked up to the test ports, it displays the S11 trace at the bottom of the screen, and not the top as I would have expected. The S21 trace displays at the bottom graticule line as well, but this is what I would expect. Is this analyzer okay, or is there a problem? I don't see anything obviously wrong with this instrument, and although it's about a year past its calibration due date, all the cal stickers are still intact. Thanks!