For best performance (2-D, SI, DI):
With the boat fully loaded, at normal operating weight, and on the water.
Side to side:Exactly level.
Front to back:It can be tilted with the front a little lower than the back.
Bear in mind too, that the attitude of the transducer will be different while at
rest and while underway.
When the bow raises (with speed), the front of the transducer tilts upward because the
stern squats deeper in the water.
This will show more of what's under the mid and front of the boat (while underway), rather than what's directly under the transom, at rest (for transom mounted transducers).