Edge 305 strangeness
 

I just noticed something weird with the 305 when I'm doing intervals on my trainer.

During the 4 minute "on" phases it shows an ascent of 6m and a descent of 6m yet during the 2 minute "off" phases the ascent/descent reads 0. Of course on the trainer in my apartment I'm at the same hight all the time.

The only explanation I can think of is during the time I'm spinning I'm riding in position so my mouth is nearer to the stem/305 and when I rest I sit up straight in the saddle. Could it be that my exhale/inhale during the "on" phase is changing the air pressure around the 305 enough to fool the altimeter?

Anyone else notice this/have a theory?

I feel that it's because you are taking your riding to new heights while doing your intervals. Don't question the numbers. Just log them like a good road weenie. Impress your friends with your ability to climb while standing still.

Why do you have your GPS on at all?

It is just the normal wobble of the earth as it orbits the sun.

It's not on. The 305 uses a barometric Altimeter so something is changing the air pressure when I spin.
There are only 3 differences between when I spin and rest:
1- I'm breathing harder closer to the 305
2- The wheel is rotating
3- My legs are moving

It has to be some sort of alternating change in pressure because I go up 6m ( less pressure ) and go down 6m ( more pressure ) so that's why I think breathing ( inhale/exhale ) is the cause. Wouldn't be the wheel because it rotates at a constant rate. Perhaps leg strokes make some kind of vortex ?

Worm holes. You're tearing the fabric of space with your awesomeness. You should be happy. I have only been able to scratch it.

You're just feeding the Garmin 305 hate group. Stop it!

Unfair. I never even posted to this thread.

I'm guessing the change is related to temperature. As you mentioned, your 305 is using barometric pressure to find altitude. When you breathe closer to the 305, you warm the air near it. The warm air is less dense, so the 305 thinks the thinner air means higher altitude.

I can't imagine how it could show any altitude changes if the GPS is off.

Setup menu>System>General>GPS>Off

All functions other than GPS will still work. Since you're inside you must be using the Speed/cadence sensor which is providing speed/cadence data.

Should probably read the thread.... GPS has nothing to do with the altitude data