red dot? if it has a meter, that red dot is exposed when you switch the meter from high-scale to low-light. There's a little switch on the top left of the housing that has the name.
If your camera does not have a meter, then it still has the red dot but no switch and no meter -- just a red dot. CONGRATULATIONS!!! Do you have any idea what leica users pay to have a red dot on their camera?
ok, being silly, but that's why the dot is there. At one point a meter could be retro-fitted.
There's no click stops on the f-stop because if you look on the left (as you are looking down at the top of the camera) wheel to adjust the shutter speeds you see a little race-track shaped thingy. When that is lined up to make a complete circle it locks in with the shutter speeds so yu can change lens/speed without changing the exposure index yu are using. To disconnect, push the center of the little race track thingy in and give it a quarter turn.
f-stops can be set at intermediate settings. Shutter speeds cannot.