I am using my own hardware using Nordic NRF51822. Although the hardware is exactly the same, the RSSI varies at 1 meter . The variation is so large that I have to separately calculate for each beacon when I calculate distance from RSSI for ranging purposes as my calculation requires Tx Power (i.e. RSSI @1 metre). Please let me know that in case of estimote do you calibrate each and every beacon. Is it why the cost is so high for estimote beacons as the hardware cost me just $3.23.