bikingshearer 

The right-hand shifter shifts the rear derailleur and has to coordinate with the number of cogs in the back - one click of shifting equals one gear up or down (as the case may be). This is true of Campy, Shimano, SRAM. There are compatibility issues between, say, Campy 9-speed and 10-speed right hand shifters because 10-sp rear cogs are thinner and closer together, so the shifter has be built to handle that. A 9sp right-hand shifter will not play nicely with a 10-sp rear derailleur and cog set. (There are after-market devices that work around this problem.) ALso, a Campy 10sp shifter will not play nocely with a Shimano 10sp rear deraiileur or cogset because Campy and Shimano make their cogs at slightly different thicknesses and space slightly different distances away from each other. This has been true for 30 years or so, and they show no signs of deciding on a single standard.

The left-hand shifter shifts the front derailleur. It does not care how many cogs are in the back. Shimano left-hand shifters are indexed: one click equals one gear up or down. I think SRAM is the same, but I've never dealt with them so I am not positive. Campy is different. It's left shifters have a bunch of clicks - I've never bothered counting them and will take somebody's word for it that there are 12. One click does not equal on chainwheel's worth of shifting - it will take some indeterminate number of clicks. You can also trim it one or two clicks' worth to bring the FD into better alignment for a given front-rear cog combination, something you cannot do with Shimano (and one major reason why I prefer Campy drivetrains, but others disagree). It is more akin to friction shifting, or maybe even more akin to Suntour power ratchets (downtube and bar end shifters intended to use with friction shifting systems). The Suntours probably have more "clicks" that a Campy Ergo left hand shifter, but it has never occurred to me to check. You could what is nominally a 9sp Campy left shifter on any Campy FD in any Campy drivetrain from at least 8 through 10 speeds and probably down to 7 and up to 11. You could even use it woth Shimano FDs with no problem at all. (I doubt but am not positive that a Shimano left shifter would not work with a Campy FD and Campy crankset because my guess is, as with RDs and cogsets, Shimano and Campy make their chainwheel an different thickness and have them a slightly different distance away from each other. (I could be wrong about this - is so, someone will be along shortly to correct me.) With the Campy system, you, not the lever, determines how far the FD moves, whereas with the Shimano system, you click once and the FD goes where it goes and you have nothing more to say about it. You can trim a Campy left Ergo shifter in a way that is simply not possible with Shimano. The only Campy issue is whether it will handle a triple up front - and that answer to that is almost always "yes," at least with 9- and 10-speed.

Sorry for the wordy explanation, and sorry if I told you a bunch of stuff yo already knew. If so, think of it as your question eliciting a response that might assist someone newer to all this.