Measuring signal strength for directional antenna

I have an GL-AR300M with external antenna, and I just bought a directional antenna, that I have pole mounted outside. Usually, I can see the AP, so pointing it roughly is easy enough, but I can’t see from the closet where the router is, so it would be very useful to see the signal strength (the dBm figure) from the AP, so that I can fine tune the pointing.

Is there a simple way to see that in the interface?

I found the answer to my own question, so posting it for future reference: LuCi has exactly what I was looking for. Moreover, it can be installed easily by going to “More settings” and then “Advanced”. LuCi has a status page, and you can even get a graph there.