WiFi icon at bottom of screen, what is it measuring?

[timmn1]

When you click on the WiFi icon at the bottom of the screen, near the date, you get a list of all the WiFi networks around you, and a percentage, exactly what is that percentage measuring?
What I've found is that the percentage number goes down when I connect to my network, sometimes between 30 and 40%. The percentage was so low on the computer downstairs that I went out and got a range extender, it connects just fine, but when I click on the icon, it reads 0% when I'm connected.
The router I'm connecting to is a tp-link Archer AX1500 in access point mode, and the WiFi network card in both computers is a Fenvi FY-2030T which is using an Intel Wireless-AC 9260 chipset. The range extender, which I'm probably going to take out because it doesn't seem to do much, is a tp-link RE603X.
The Router is upstairs, and the computer upstairs is about 10 feet away from it, the computer downstairs is located almost directly below the router.

[vimes666]

Most routers shout their name as loud as they can, but as soon as there is a connection it will lower the power towards that connection to a reasonable level to avoid cross interference. Did you have a bad or slow connection?