@ Dave(52 re 511A. Way back when, when I was a wee engineer, I bought a surplus 511AD from my EE department as surplus. It was a cool scope, but was way more seat of the pants waveform visualization than my 555 I own now. I ended up giving the 511 to an EE friend at work long ago when someone sold their RM 54ty something scope with a plugin compartment! I had arrived!