The hourly contacts shows 24 bars, one for each hour in the past 24 hours. You can swipe left and right to pan. The height of the bar shows the number of other GCG users who were within Bluetooth range in that hour. The color indicates the duration for which those many users were within Bluetooth range. This duration falls in 3 buckets: <10mins; ≥10 but ≤20mins; and >20mins.
Note that these bars do not consider how close those users were to you. For that, we shows a line plot overlay which indicates the number of GCG users who were estimated to be within 2 meters of you for a cumulative of 15 mins or more in that hour. Keep this number low.
Note that both the contact counts and the distances can both over- and under-estimate. Sometimes, users can be detected even 20+ feet away, while scans may be missed from even nearby users. We use the signal strength of Bluetooth advertisements from other phones running the GCG App to approximate distances. While the signal strength typically attenuates with distance, it is also affected by factors such as phone model and hardware, casing, reflective surfaces, surroundings, etc. Bluetooth advertisements can also be picked up when two nearby phones are separated by a physical partition such as wall.
We are researching on estimating these distances more accurately in lab settings. Please let us know if you find these estimates to be grossly inaccurate.