I have just got a Gould 465 DSO (same as 420 & 450 but 100MHz bandwidth).
With the input grounded the trace is never dead straight (as with an analogue scope) but exhibits a very, very tiny amount of vertical noise. It doesn't alter with channel sensitivity and is the same on both channels, so I'm guessing it's due to ADC error. Everything else about the scope works perfectly.
It's livable with but if anyone can tell me whether this is normal behaviour for these scopes (or other DSOs in general) I'd appreciate it.
Bob