Holux M-241 data readout

Hello,
Just got some Holux M-241 units for a project in Mali (W. Africa).
I'm using the units on tethered helium balloons mostly for altitude data (as they are very light-weight).
Looking at the data it looks like both the altitude and long/lat are off.
I'm not sure if there was some calibration I needed to do first or what. Not clear from Holux online manual...
I know the height of the topography is about 300m ASL but the GPS data is between 115-550 m. Our balloon only goes to 250-300 m above the ground.
Looking at the long/lat data on GoogleEarth I see a totally different location than where we were working from too. Not sure why... I tried changing the GE settings to decimal degree also - still off by some 20 km and 45 degrees from our location...
Any suggestions?
Thanks very much!
Roy.