Campagnolo's EPS Interface Unit is like a translator, the vital but often overlooked piece of the electronic shifting puzzle. Mounted to the brake cable or the handlebar, it processes the data churned out by the EPS Power Unit (sold separately) and communicates it to you via an easy-to-read colored LED. Plus, it plays the critical role of converting every analog shift you send its way into a digital format so the system can work as a cohesive whole. There's also an easy-to-read LED battery gauge so you know when it's time to recharge the system. Oh, and doesn't mind the weather, as it's totally waterproof.