My friend gave me a fully functional antique frequency counter. I don't need it with my oscopes and spectrum analyzers, but you have to admit this thing is pretty sexy.
I'm pumping a 12 millivolt peak-to-peak sine wave into this thing at 10MHZ. That seems to be the bottom of it's resolution range. Much below that and the counter drifts. Not sure if that's the counter or my equipment though. I am using a cheap signal generator for this test.