What do English people call the old wooden yardsticks that folded up onto itself to 6inch final length

I believe it's a "yardstick", no less, choupette

Occurs to me that a rule of thumb is really a ruler of thumb, and the important thing is that it is an inexact measurement, approximation, "near as dammit" thing. If you had the same carpenter/builder constructing something in its entirety, you could use the size of their extremities as measurements without everything going pear-shaped (non-Brit equivalents, folks?) - but once there is more than one person involved in the construction, you simply have to standardise.

Fisk