Not a bad little app ...

Not a professional land surveyor so i cant comment a 100% on its accuracy - but - just a couple of touch points i measured using it & then comparing it to what i could find using google searches - seems to be fairly accurate. Bought it specifically to set my Citizen watch which has a builtin altimeter - needs to be set initially & then it calculates its own values - the two seem to get along nicely - so again - it seems to be fairly accurate (the app)

Cold Canadian In Texas about Altimeter+