Name: Gear Inch auto calc using GPS for speed & cadance
Author: shprung

I mostly ride a fixed gear bike, and instead of using a gear-ratio calc app or anything online I wanted real time info from my Garmin Edge 820, 
so I wrote this data field that shows your gear inch (and 2 supporting values: your cadence rpm and speed in mph. 
It is designed to be placed in a full-width-field like I showed in the images below.

You have to have a cadence sensor for the gear-inch to be calculated. 
Because the speed is not "perfect", it uses the GPS, the gear-inch number will change a bit +/- 1 inches but you clearly get the gear-inch value.

It is nice to see gear inches on a gear bike as you change gears so you can see what is going on. 
For example, you can see if the small ring gives you less inches than if you put it on the big ring and a different gear in the back, etc.