Decades ago, my brother Kevin took me and my wife out on Lake Washington in his new sailboat. He was testing out equipment including a depth finder. We were sailing toward the eastern shore between the two floating bridges. We seemed to be getting too close to land but the depth finder still registered twenty feet and continued to register twenty feet as we ran aground in shallow water. Apparently it was set to register no less than 20 feet. Maybe that was the danger zone where further information is superfluous like if the altimeter on your jet airplane gets down to twenty feet. I never learned depth finder details because I avoided that sailboat as if it were a time share condominium. I have always wondered how far my brother or anyone else would have trusted that depth finder if it had been physically possible to run the boat onto the beach, into the parking lot, and up to Snoqualmie Pass.