well this is ... what is it? a capo with built-in open-tuning, sort of? all truely analogue, they were tied to the fretboard of a guitar:
from what i found on the net, they were invented in the 20s and produced well into the 60s (they come up on ebay regularly) and were initially built for people unable or too lazy to learn chording. pretty weird idea, i guess ...
i suppose one could do some cool things with these ...
