How to measure RSSI of bluetooth devices on PC
"Signal Strength" != RSSI.

RSSI is an indicator for how well receivable a receiver considers a signal – that's typically not inherently dominated by the signal strength, but by factors like noise and interference.

Thus, it's a device-specific estimate for how well the bluetooth device is able to receive someone else. Nothing more, nothing less. Be careful in your report not to completely conflate it with signal strength. If everything else stays constant (mainly: the other things using the 2.4 GHz band), then, however, RSSI will at least for the most part be proportional with some unknowable factor to received signal strength.

Bluetooth interface devices communicate with the host computer through a protocol called HCI. That's pretty standard, and it even offers a command to read the RSSI of a logical bluetooth connection. 

I'm thus very surprised it should be hard under Windows or OS X to get an RSSI estimate using "on-board tools"; but then again, I'm an engineer and never use Windows for anything technical...

Under Linux, it'd be trivial to get the RSSI after connecting to a pairing partner device:

hcitool rssi AA:BB:CC:DD:EE..


where you of course replace the AA:.. string with the bt address of your connection.

hcitool is super handy. Quite possibly hcitool scan already contains all you want; hcitool lescan if you want to work with Bluetooth Low Energy beacons; hcidump --raw will simply print out all the packets flying by after triggering a scan, including info about RSSI.

(You can get a live USB Linux image that you don't have to install to anything; you'd just write it to a USB stick and boot your PC/laptop from it, and then would have a working Linux system without touching your main system.)