Barometer/Altitude calibration for outdoor usage

Using a barometer for altitude computation is a very nice feature for outdoor/mountain activities, because there often are situations where GPS signal is not available or, during a long hike, you need to switch GPS off most of the time in order to save battery.
I appreciate very much the support of the barometers available in Oruxmaps. However, one cannot derive a usable altitude value from the pressure without any calibration. In the calibration process the user might input several well-known values, like
temperature, altitude, or sea-level pressure. For a more convenient usage of the barometric altitude display in outdoor activities I suggest to built in the following altitude calibration feature: A user provides his real current altitude (coming some different source, e.g. map, GPS etc.). The difference between the real value and the value derived from current pressure is then used in oruxmaps to compute a more exact altitude value for the trip. An easy method might be to just add the difference between both altitude values.

Some barometer apps allow for calibration, but they require the user to supply the current sea level pressure. Being outdoor, you probably don´t have pressure values from other sources than your android device.
Thus you need to repeatedly input estimated sea level pressure values and look at the derived altitude values, until the derived altitude corresponds to your known real altitude. This is very clumsy.

Thanks, and Keep on the good work!

Mike