RSSI to Distance Conversion

gistfile1.js

function calculateDistance(rssi) {
  
  var txPower = -59 //hard coded power value. Usually ranges between -59 to -65
  
  if (rssi == 0) {
    return -1.0; 
  }

  var ratio = rssi*1.0/txPower;
  if (ratio < 1.0) {
    return Math.pow(ratio,10);
  }
  else {
    var distance =  (0.89976)*Math.pow(ratio,7.7095) + 0.111;    
    return distance;
  }
}