Pro Altimeter is actually the most accurate Altimeter on the Android market (up to +/- 10 cm with barometric
sensor) for sports and leisure activities.
The measurement provided by the GPS receiver is Geoid compensated and will improve its accuracy after a few minutes, depending on atmospheric conditions.
If your smartphone or tablet is equipped with a barometric sensor, and if you take care of calibrating the QNH (barometric pressure corrected), you will obtain a very high accuracy.
A time graph allows you to track the variation of the altitude.
You can choose the refreshing frequency of measurements and graph that suits you best depends on your activity.