Originally Posted by Drew Eckhardt

In response to Shimano's lightened DuraAce calipers for the 2001 model year Campagnolo introduced a "differential" brake option with dual pivot front and single pivot rear saving 40g a pair (380->340g a pair for Chorus, 348->308g for Record which is identical except some of the hardware is titanium where it's steel for Chorus).

The rear single-pivot unit is on the left and front dual-pivot right.



The single pivot option offers a bit more tire clearance and the 2001-2006 Chorus/Record hidden hardware single pivot rear looks great, although outside a very narrow range of competitive situations the only substantial benefit is marketing.

Supposedly the rear is easier to modulate because the lever travels farther although I haven't found that to be significant. It does take a harder squeeze to lock up.