How deep should you deploy your Side-looker? SonTek side-lookers’ beams spread as they move away from the system. Installations should use the aspect ratio of 1:20 as a general rule of thumb. This means that for every 1 ft of water above or below an instrument that isn’t a boundary (surface or bed), the instrument can profile 20 ft horizontally without top/ bottom interference. The best way to check that you have installed the system properly is to look at the Beam Check to make sure there are no peaks from reflections where you don’t expect them.