how is RSSI measured?

[bluebeam]

I have nRF52 on both central and peripheral. I'm getting the RSSI value on the central by looking at the RSSI field in the ADV_REPORT event. I see the RSSI values has a wide range, even when the peripheral is just put still in front of the central. Looks like it generally have 6dbm fluctuation. Is that expected? Is that because it's measured on different adv channel? How reliable is it to be used as an indication of distance? Thanks!

rssi-sample2.PNG

[endnode]

In other words your plot with having +-5dBm variations is perfectly fine even for "near to laboratory" static environment, actually once the signal gets weaker below -80dBm it's absolutely normal to see +-10dBm fluctuations or even more.