It's mainly for stick steer boats that run one Humminbird unit and 2 transducers(one on the front and one one back). You can also use it to run a side-image TD and thru-hull TD on on the consoloe unit. You put it on A while using your SI and when you get ready to run, you put it B for your puck TD. The units ending in 7 uses an A/B switch. The 8 units change automatically. And I didn't have to ask Wannabe for information.