BEAT PROOF switch

Can anyone tell me what it is for?
Its on most of my boxes and it seems to do nothing.
Thanks

It's to eliminate interference when recording an AM broadcast.

Some boxes label it "OSC" or "Beat Cut"

As described above, that's what it's for. Some time ago people would record talk radio off the AM stations. The beat cancel or 1- 2 switch would help eliminate another station's interference. Otherwise its mostly useless in everyday life. Hey, its another button that looks cool to have! More gadgets the better

Ok
Thanks guys!!