The back porch light stopped working, a new bulb didn't help.

So. I put a meter on the socket. 0 V.

I pulled the switch plate off (just a normal single pole). 80 V
terminal to terminal. Hmmm?

Killed the power, put an ohmeter terminal to terminal, infinite
resistance at both switch positions. Diagnosis bad switch, supported
by the fact that before it died completely, flipping the switch
several times made it work. Besides I've always had a CFL in that one
and I suspect the capacitor shortens the switch life due to arcing.

Okay, a new switch is $1.29, no big loss if wrong. Took the old
switch off, turned the power back on and checked wire to wire just for
grins, still 80 V. Uh oh.

Put the new switch in. Turned power on, checked the socket, 120 V.
Put bulb in, (CFL), lights up fine.

Well, I have a working porch light again, but I'm left with the 80 V
mystery. I don't know any way to get 80 V on a normal residential
power setup. The meter was a digital Radio Shack multimeter. If I'd
had time I'd have checked again with the Simpson analog, digitals
sometimes give funny readings, but I've never seen 80 V. What am I
missing?