To help me find the temperature breaks where game fish congregate, I installed a Si-Tex SST-110, the Gucci of sea-surface-temperature gauges. The 4.3-inch square SST-110 offers a large display, and it carries readings out to two decimal points. It installs in a standard 2-inch gauge hole. The through-hull sensor requires a ½-inch hole in the hull, but it is more accurate as a result of its size. You can also calibrate the temp. I used a National Sanitation Foundation International-approved reference thermometer ($20 online) to verify the SST-110's accuracy. $319.95 (with bronze through-hull sensor).