I'm working with Estimote beacon from some weeks but I have a doubt. What is the unit of measurement of the Estimote's distance?
NSString *distance=[NSString stringWithFormat:@"%@",beacon.distance];
If I place the Estimote at 10 cm from the iOS device the distance is 0.055.
You can not calculate the exact distance - prove. It is rather some indication (but not too strict) whether you are getting closer or not to the beacon.
Morover, according to Apple's documentation:
"The array of beacons is ordered by approximate distance from the device, with the closest beacons at the beginning of the array. You can use the information in these objects to determine the proximity of each beacon and its identifying information (proximity UUID, major, and minor values). For instance, the value of the proximity property of the CLBeacon gives a general sense of the relative distance to a beacon."
And to be honest I haven't found any information about the units, it is rather a value to distinguish somehow the relative distance to that devices.
ANSWER: it is not any specific unit but only a relative value (still worth to read above text)