I tried using Google map to work out my elevation, but it didn't work for me.
When I clicked on a location a few kilometres away from my house, it had the altitude as 45 metres - in the middle of the ocean! I tried this several times, but still got the same reading.
The reading for my house was 8 metres. I subsequently bought a Polar S725 and calibrated the altitude at sea level - my house actually has an altitude of64 metres - that's quite a discrepancy!
I'm not sure if this is because NZ isn't properly covered by GoogleMaps yet - although my particular area was pretty well detailed.