Etrex Vista C vs Polar 720i Altimter

Hi, I use an Etrex Vista C as my (world's greatest) bik computer. I also use a Polar 720i HRM. The total ascent is consistently 15% higher on my Etrex GPS than my Polar.

Any opinions on which to trust?

 

I dont know the Etrex, but I know about Polar, it uses air presure so any important variation in the pressure can give you imprecise reads. An interesting explanation it's here

http://support.polar.fi/PKBSupport.nsf/ALLDOCS/42256C2B001E0F6A42256B0B0034E39D?OpenDocument

As a general observation that I made from the use, Polar it's good measuring height differences, but if your base altitude it's wrong, the hole graphic mantains the error in a consistent way.

I would vote for the GPS technology.

 

You might also look at the Datum your Vista is using. The Datum is an agreement on what sea level is, and a bunch of other measurements.

It is found under Setup I believe. I usually run NAD 81, but you can try NAD 29 as well.

Robbie