I often joke about this, but I really can judge the temperature outside from my armchair. Looking out through the glass doors I can see the Purple Sprouting Broccoli plants, and the position of their leaves gives me a good indication of the temperature.
If they are upright like this, the air is relatively warm:
Whereas if they are drooping downwards like this, it is cold - below freezing temperature!
When the leaves droop, the flower-head remains upright and is therefore much more visible.
This one is "Rudolph", and you can see that it won't be long before I can pick some spears from it.
The central flower-head of "Red Spear" has yet to form, but the side-shoots are getting bigger very rapidly.
OK, here's a test for you: what temperature is it in the photo below?
You probably guessed, we got our first frost of the year at the weekend. I would say it's about a month later than usual.