Unzip the contents of "GameData" to your GameData folder, same as with most mods.
KSP 1.7 introduces a new feature that allows toggling the altimeter between "ASL" mode (height above sea level, i.e. what it's always been since the dawn of KSP) and "AGL" mode (height above ground level-- this is the new KSP 1.7 feature). All you need to do to toggle between the two is to click on the little blue-or-green button on the left end of the altimeter. It's a great feature, very handy, and one that KSP players have wanted for a long time.
I'm really happy about it... but I'm also very lazy. I'd like it to just automatically set to ASL or AGL based on what's "right" for the current situation, so that I don't have to mess with it. On the other hand... I still want to be able to switch it manually whenever I want, since "special circumstances" can always come up where I need to decide on my own what to set it to.
Well, this mod takes care of all that. It just automatically sets the altimeter to the "right" mode (more on what this means, below) based on the ship's current situation, but the player can still manually toggle as desired and the mod will respect that.
Here's what the mod does, by default (though note that you can customize via settings, see below):
"Low" is defined as follows, by default (again, see customization options below):
The practical upshot of this is that on Kerbin, the altitude boundary between ASL and AGL modes will be a bit under 500 meters if you're close to sea level (e.g. at KSC), somewhat higher if you're over higher-altitude terrain. If you're falling rapidly, it'll be higher still. If you have any active parachutes, it'll be 2000 meters (i.e. twice the parachute's activation altitude, assuming you've got it set to the default 1000m).
It "just works". It switches to the mode you choose, and stays that way without automatically switching back. However, it'll later revert to automatic mode when circumstances are "appropriate". Nitty-gritty details in KSP forum thread if you're curious, but the practical upshot is that it "just works" and does pretty much what you'd want it to.
The default behavior is tweaked to be the way that I, personally, like it, since it's my mod.
However, the mod provides configuration settings in the KSP settings dialog:
Here's a rundown of the options available:
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