Ride elevation variability

I was watching CVR world cup webcasts and noticing the variability in elevation gains reported by different riders who were finishing, having ridden the exact same course (4xGreater London Flat).  Some were showing 150m, some over 180m.

I’ve noticed this as well comparing some of my rides to some of the elevation gains in courses reported by Zwift here: https://support.zwift.com/hc/en-us/articles/213336506-Zwift-Courses-and-Routes

Why does this variability exist?

Interesting point! Reminds me of the variation I get when I go for outdoor rides–same route, different elevation gain each time. Here are some thoughts:

• Maybe the random changes in positioning of the rider laterally across the road accounts for some of the variation.

• If elevation gain is measured from sea level, then if you start a ride during high tide and end during low tide, you’ll gain an extra bit depending on the tide cycle in Watopia (in case it’s not obvious, this one is a joke…).

- But the most likely answer is that each rider’s elevation gain is being calculated in real-time by multi-input algorithms that have rounding errors that are propagated disproportionately based on the speed, position, and sampling points of individual riders.

Not sure any of these would account for riders having 150 m vs. 180 m on the same course, but could explain some of the variation you’re seeing. I’ll be interested to hear others’ thoughts.