1.First you should understand that RSSI is influenced by different factors. So measuring distance using it is not always reliable. 2.For discovering errors in distance measurement using RSSI you can do the following. 2.1 Distance for various values of RSSI values are first determined using the prevailing models. 2.2 Actual distance is then measured (simultaneously with RSSI) 2.3 RMS errors play a significant role in this aspect Comparison of data can then allow you to find out the errors in distance measurement. 2.4 Do note that new statistical methods are being developed for this purpose.