Not that it really matters, but.....
14.7:1 is called Stoich. It is based on "ideal" from an emmissions standpoint only. All emmissions controlled cars are tuned to run at or near that ratio so that the converters function properly and emissions are lowest.
15.5:1 is actually the best for fuel economy, but NOx emmissions will be higher and the converters will not work properly.
Your computer does not ever run at 14.7:1. What it does instead is switch back and forth between about 16:1 and 12:1 continually as you drive. The blinky lights as the EEC switches back and forth will either drive you nuts or you will learn to like it.
Under WOT conditions a naturally aspirated motor likes to see about 13.5:1 (richer than stoich), and a boosted motor like ours likes to see about 12:1. Our motors are typically tuned from the factory to run at about 9.5-11:1 under WOT, which is beyond the ability of the gauge you are looking at buying to read (too rich). So the gauge is neat, but kind of worthless.
A WB02 gauge is useful because it reads from 17:1 - 10:1, but are expensive ($350) and don't come with that neat round gauge face. They are typically a hand-held digital device.