Originally Posted by
gsa103
...
A standard GPS unit has a vertical accuracy of about 10m vs about 3m for lat/long. Barometric altitude is more sensitive for small changes in elevation, ...
For a bicycle, barometric altitude will give you a better estimate of elevation gain & loss, but potentially less accurate for the absolute altitude, such as the top of a hill.
100 feet is a much larger "noise" signal on successive elevation measurements than 10 feet is on successive horizontal measurements.
The impact of the error on gain is also larger than on horizontal displacement given that the gain is based on much smaller differences. It's even worse because the vertical speed is much lower, generally, than horizontal.
GPS might be ok for casual absolute elevation. But not many cyclists are interested in that.