What are you thinking? I've downloaded the ride notes app and the heart rate colour apps for my 520.
I've had one or two ideas that I'd like to try out. Nothing groundbreaking, but they'd keep me out of trouble.
The easiest to make happen would be a gear indicator that beeped if you'd crossed your chain. My local area doesn't have the big climbs but lots of short-sharp stuff, so I'm up and down the gears like Richard Clayderman. I hate crossing my chain but seem to do it all the time, so an idiot beeper would help without taking up any screen real-estate. The IQ API doesn't give access to Di2 gear info but others have managed to estimate gears from speed and cadence so I'm sure I could have a stab at this part, but I still wouldn't be able to emit a sound as this isn't supported for Edge devices.
Next on the list was a hill category/score indicator, based on the Strava method, but this is where the Edge-supported API gets silly in that it doesn't give access to the elevation figure, only the total ascent and descent. I've tried back-deriving a gradient from these and, although it's doable in theory the gradients are badly out, I think due to the way the Edge algorithm that determines ascent or descent. It might work on longer climbs where the oddities of the ascent algorithm should get smoothed out, but see short-sharp stuff above.
Further down the list was a crude estimate of aerodynamic efficiency - something like a CdA - based on power output, bike/rider weight etc, but this would need gradient again to be useful on all but he flattest of courses.
There are a few more things I'd like to try to they're all knackered at birth because position isn't accessible either. Sort it out Garmin!
