What about it? I don't find anything with that name in the USA app store.
I think that means Watch Altimeter Pro. I don't have this app, it costs money, but to me one of the key considerations for any of these apps is do they use the GPS to determine altitude or the barometer? I can't tell for sure, but my guess is this uses the GPS. Wasn't the barometer new with Series 3 (and so any app that works the same with S2 is using GPS?). GPS is ok, but is not going to be nearly as accurate for changes to altitude as the barometer.
As for working independently of the phone, 2 of the apps mentioned already, that I have, do work independently. So Up High and Barometer and Altimeter Pro work separately from the phone.
I went back out to my hill and ran up and down it 4 times to retest these 3 apps and so edited the info above.
Altimeter+ is a cool iphone app. Useful for hiking on the phone. Offers GPS, Aster and barometer for tracking. But does not work independently on the watch and is not really useful in my view as a primary watch app.
Barometer and Altimeter Pro: is a cool iphone app for a barometer. It can track trends over days and weeks, but only if you use, so the data points on the phone are only for when you check the barometer on that day/time. It does work on the watch but two key things: first it does not maintain focus, meaning the watch will return to the clock display each time, so you have to navigate back to this app. Also #2: I think this app just uses the GPS for altitude; the barometer readings don't mean anything to me, but the altitude seems to bounce around up and down, just like the variation I see on a GPS. So the bottom of the hill is sometimes higher than the top.
Up High: when I turn on tracking of relative elevation, it maintains focus and tracks elevation, but only change from that starting point, and so not cumulative elevation gained in any way. Up High works independently on the watch and refreshes the altitude within 1-3 secs at a glance, so more than fast enough to be useful at a glance. My only wish was that the font was bigger or I could swap the barometer reading with the altitude (since the B reading is in large font).