The only way to estimate distance to a beacon is based on measuring its signal strength. However, the Received Signal Strength Indicator (RSSI) value alone does not mean anything, because beacons can broadcast their advertising packets with different TX power. For example, a smartphone should report RSSIs in different ranges for two beacons located in the same distance from a user, but broadcasting with different TX power levels.
To address this issue beacon advertising packets, in addition to payload with identifiers, also broadcast reference RSSI values. For iBeacon it's the RSSI at 1 meter and for Eddystone it's the RSSI at 0 meters. This way an application that tries to estimate a distance to a beacon knows what RSSI it should receive at a certain distance to a beacon. Then, using it together with the actual RSSI, apps can extrapolate a possible distance to a beacon.
Originally, Kontakt.io provided only beacons with precalibrated RSSI@1m and RSSI@0m values that were suitable for most use cases. However, to accommodate more diverse deployments we've recently introduced the Reference RSSI Value Calibration.
Right now, everyone can do their own measurements to calibrate their beacons. This parameter is configurable from the Kio Cloud Device Management app as well as via our Device Management API.