This can be viewed as a TECH NOTE for the cycle computer manufacturers as well as the GPS manufacturers.
Last week I was testing several different GPS head units and cycle computers that ‘talk to’ Di2. But, after comparing the data, I noticed that something just wasn’t right. But let me take a step back. The Shimano D-fly wireless transmitter sends several pieces of data to ANT+ devices. These data of importance being Di2 battery level and gear position (front gear number, rear gear number). Its up to the cycle computer/GPS to take this data and display it in a value added format such as a graphical representation of what gears you are currently in and by recording time stamps, can tell the cyclist what % of the ride he/she was in what gear.
So what’s the issue? After entering (a) Cassette Model 9/10/11, (b) Cassette type (11-23, 11-25, 11-28, etc.), and (c) Crankset Type (50-34, 53-39, etc.) into your cycle computer/GPS, it has enough information to display all kinds of data for you. And that’s the issue. In this example, let’s say you have a 50-34 Crankset and a 12-28 cassette. Furthermore, let’s say the EWW01 transmits 34-28 to your cycle computer. Is 34 gear #1 or gear #2? Is 28 gear #1 or gear #11? Should the cycle computer display 1-11 or 2-11 or 1-1 or 2-1? Left to right or right to left for both front and rear.
A call into my sources confirmed that Shimano numbers the gears LEFT to RIGHT, 1 .. N.
Please see graphic to the right