That's a shift lever to go with the Portacatena set up that had a chain hanger that attached to the inside of the rear drive side Campag dropout. Pushing that button allows the derailleur to move the chain just that much more to drop onto the hanger, making wheel changes easier.
Didn't last long, maybe 1978 - 1982. On bikes of that era, you'll sometimes see the dropout with two little threaded holes that the hanger affixed to.
John Siemsen Portland, Oregon
Message: 5 Date: Thu, 21 Jan 2010 09:10:26 -0800 From: Dave Abraham <daviabraham@yahoo.com> Subject: [CR] eBay outing: CAmpi S/L, no connection To: <classicrendezvous@bikelist.org> Message-ID: <661646.20895.qm@web54001.mail.re2.yahoo.com> Content-Type: text/plain; charset="us-ascii"
I've never seen this
Dave Abraham New Wheel ~ Hokie Spokes http://www.hokiespokes.com Beautiful SW Va. voice: (540) 552-SPOKe (7765) & 731-1211