This app calculate de Geoid Undulation using EGM2008 2.5'x2.5' grid
This app calculate Geoid Undulation using EGM2008 2.5'x2.5' grid http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008/egm08_wgs84.html interpolating it with CSPLINES Piecewise Bi-interpolator from Apache Commons Math 3.6.
It's works offline so you don't need be connected to use it.
It's only needed be connected to download it from play store.