Re: Corrona App - Whats the rest of the story ?
As for rangefinding, it looks sketchy. Bluetooth low energy has no feature for measuring distance leaving measuring signal strength aka RSSI as a crude proxy for that. Probably all are passing transmit power to improve the calculation, many will be using some form of per-type calibration but possibly not a complete tx/rx model, few appear to be using heuristics to try to determine if they are inside/outside buildings or inside bags/pockets which are critical factors. I doubt any are looking at channel numbers (frequencies) to see if there's scope for improving the accuracy there.
An independent review of the results from one of the large scale controlled trials would be very interesting to see how accurate the proximity data is. Unfortunately, I doubt we will be allowed to see that.
Biting the hand that feeds IT
