It's not a computer, but it's surely over 10 years old... I got a scope today, a Tektronix either a 535a or 545a according to the operator's handbook in the little hidey hole in the top of the case. (which I'll gladly scan if anyone wants a copy). So I'm a 'scope newbie, does the probe impedance (13 pf) have to match the rating on the jack on the scope (47 pf) for the waves coming out of the calibration jack to be properly square? And if so, does anyone have a source for probes that work with ancient scopes like this? Also, how do I tell a 535a from a 545a? Other than the waveform distortion (at worst the square waves wind up looking like shark teeth, and at best they're a bit sloped on the leading and top edges) the scope seems to work fine as far as I can tell. Also, can anyone recommend a good book on scope use for newbies? -- Jim Strickland jim(a)DIESPAMMERSCUMcalico.litterbox.com ----------------------------------------------------------------------- BeOS Powered! -----------------------------------------------------------------------