I have E71 and use it with LD-4W external GPS.
When measuring altitude I can compare the build in program with the NST.
The build in program is +/- 5 meters.
The NST is always at least 20 meters higher.
This should be fixed next version.
E71 + LD-4W user
Lat: 31.80244N Lon: 35.15630
I'm using the Nokia N85 and my altitude measurements are hilariously inaccurate. I live at or near sea level, and NST frequently tells me I'm fifteen or more meters below sea level.
Running underwater is hard work, I tell ya what.
GPS altitudes can be very inaccurate depending your place on the globe. As the globe is not a perfect ball, models are being used (wgs84 is the most common used in gps devices) so your altitude is always referenced to the wgs84 spherical ellipsoid and that's why sealevel is not a reference. Anyway what would you do at high and/or low tide? Some places on earth have more than 40m altitude difference between high and low tide...
Absolute differences in altitude should be more accurate as the gps signal is stronger (better/more satellite connections). Although I sometimes have more than 80m altitude difference in sportstracker while I don't know any hills of that altitude in my area, everything is flat here...