Weird (Incorrect?) Slope Graph

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JRandomUser
Posts: 6
Joined: Thu May 09, 2019 4:20 pm

Weird (Incorrect?) Slope Graph

Post by JRandomUser »

The slope graph in Isaac doesn't make sense to me, and I don't know if it's incorrect, or if it's displaying something other than slope as I understand it.

See the screen capture and attached ride - neither the sign or the magnitude of the slope match the actual grade of the hills at any point. For example, at the selected point in the ride, I was nearing the top of a short hill - the actual slope was positive, as the Isaac altitude plot shows, but the slope graph shows a slight negative value. The status bar at the bottom on the other hand gives a more reasonable slope value of 6.2%.

Can anyone explain to me:
  • Could the real time power reported by my PowerPod or the various power calculations offered by Isaac be invalidated by these odd values reported for slope?
  • Should I be concerned that altitude is negative for my entire ride? (I live in a low part of the world, but this ride was definitely conducted entirely above sea level!). My starting altitude would actually have been around 35 meters, but I can't see any way to calibrate altitude on the PowerPod before a ride.
  • Do I need to re-calibrate my PowerPod? If the tilt calibration is wrong, is there a way to simply override it manually with estimated values, rather than doing another calibration ride?
Thanks
Attachments
iBike_07_14_2019_1007_20_km.ibr
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Isaac Slope Display.PNG
Isaac Slope Display.PNG (204.35 KiB) Viewed 2461 times
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: Weird (Incorrect?) Slope Graph

Post by Velocomp »

Look at the top right of your main window, above your power graph.

You have averaging set to 20 minutes. So, the slope graph in the bottom is the average slope of the prior 20 minutes!

Set your averaging to 5 seconds and you will see good results (see attached).

Absolute elevation is irrelevant; the purpose of the baro sensor is to measure elevation changes, which look fine in your file.
Attachments
Screen Shot 2019-07-14 at 5.42.50 PM.png
Screen Shot 2019-07-14 at 5.42.50 PM.png (197.04 KiB) Viewed 2443 times
Screen Shot 2019-07-14 at 5.42.35 PM.png
Screen Shot 2019-07-14 at 5.42.35 PM.png (146.77 KiB) Viewed 2443 times
John Hamann
JRandomUser
Posts: 6
Joined: Thu May 09, 2019 4:20 pm

Re: Weird (Incorrect?) Slope Graph

Post by JRandomUser »

Thanks John - that explains it!
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