My Hummingbird 788ci, even with current available software upgrades and lakemaster card installed will not let lake level adjust beyond 30 feet up or down so be careful to make sure your particular unit will be able to utilize the lakemaster fully, Although there are ways to manipulate the sonar unit to be more effective at finding whales before you are on top of them, it still is not as good as current level contour lines. The three times I communicated with Hummingbird about installing lakemaster I was not told that my 788 would only adjust 30 feet even though I made it clear I was on a lake with 100' swings. Oh well, buyer beware. That being said, I would still buy a Hummingbird, probably Helix series.