I have one (GLL 2) very much like the first one. It can shoot lines vertically, horizontally and and both, crossline, I expect is what it is called. Mine also came with an attachment for holding it and mounting it on a tripod. Very handy.
I used it to stake out level lines in my yard for filling a depression that puddled water. Used it inside my garage/shop for setting up shelf brackets, but that required clamping it to a tall ladder.
The one I have is self leveling. I expect most if not have that as I don't know how else it could function.
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