How long was the Red Rock Marathon

I don’t trust my GPS watch to be accurate. More often than not it tells me I’ve run about 1% further than an accurately measured course on the road (I assume this is an inaccuracy in the GPS (or how the watch interprets the GPS over time), but maybe I run zig-zags).

Anyway I didn’t trust my watch to give an accurate reading for the actual distance of the red rock marathon. So I thought I’d collect the readings from some friends’ watches to see how they compared.

They gave me altitude readings too, which were even more different (distances in miles, cumulative elevation gain in feet, “Fr” stands for Garmin ForeRunner):

Name Watch type Website
App
Distance Elevation
Nash Fr 10 25.24mi 9715ft
Andreas Fr 10 25.2mi 9854ft
Monica Fr 10 25.3mi 9920ft
George Fr 305 GTC 25.54mi 9263ft
Brett Fr 310 Plus 3 25.89mi 6085ft
Garmin Connect 7094ft
Strava 7413ft
Heidi Fr 310xt 25.61mi 7065ft
Andrejs Fr 910xt Strava 24.9mi 6050ft

Everyone ran essentially the same course, and so essentially the same distance (and elevation). We all started within seconds of one another so atmospheric conditions should have been comparable.

Watches do not calculate elevation gain (just current elevation), that is done by the website/application which processes the data. I used “Garmin Training Center”, GTC, a stand alone App from Garmin myself.

Jon Zaid tells me the 310 watches use a barometric altimeter as well as GPS, this would be more accurate.

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3 Responses to “How long was the Red Rock Marathon”

  1. Dave Long Says:

    When we wanted more accurate altitude readings we incorporated barometric pressure input in the filter. (An alternative, if you don’t care about real-time, is to clamp the reported horizontal GPS track to a DEM)

    -Dave

    Le 26 nov. 13 à 14:22, Georges Meanderings a écrit :

    >

  2. andrejs Says:

    Mine was just shy of 25 miles and 6500ft of gain. I used the 910xt and I believe it has the barometric altimeter.. http://app.strava.com/activities/96966499/overview

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