A turn is a full 360 degrees. Turning the screws in makes the fuel mix leaner, turnign the screws out makes it richer. When adjusting the screws, I usually turn out until it starts to run rough in 1/8 turn increments waiting at least 30 seconds before adjusting again, and then turning it in the same way until it runs rough again, and split the difference. Oh and turning it it until "seated" is snug or finger tight only, not wrenched as tight as possible. You probably knew that, but just in case.