I have the same model#. There is a left and a right button. This toggles through the options. Mine has 4 buttons total. Power, hold, and the left and right arrows. The arrows let you choose which surface. I went out to my boat just now and with the soft wood setting I got about 2% on the sides of the hull and anywhere from 11-25% on the transom but it was raining and the boat was a little wet in spots. Will try again on a dry day. Just pulled it and brought it home the other day. No bottom paint on it but there is alot of algae and growth that I haven't cleaned off yet and this is where I got the higher readings. Will check again when it is dry then again after I clean the algae off to see the difference.