If you get to know the different types of cloud, you can start to predict when it might rain. However, if you want to know how sunny it is going to be then you need to know the amount of cloud.
Cloud amount is measured in oktas.
Think of some other words that start with the same sound…
Octagon. Octapus. Octave.
The spelling is different but the sound is the same and they all come from the same Greek word meaning eight.
So cloud amount is given by how many eighths of the sky are covered by cloud.
No cloud at all is zero oktas and completely cloudy is 8 oktas.
It’s judging the ones in between that can be a bit tricky, especially as clouds usually come in very irregular shapes.
Unfortunately there isn’t some nifty measure, that you can wave in the air, that will tell you the answer. You have to crane your neck, look around and give it your best judgement. And if your friend has a slightly different opinion, there is no easy way of proving who is right.