In article ,
Lee writes:
The B&Q set we have does remember, if the button is held pressed for 10
secs when on the selected mode - no mention of this in the
"instructions" of course.

There's almost certainly some type of delay before saving
to non-volatile memory, because the NVRAM in many of the tiny
cheap microcontrollers can only be written a relatively few
times, and if it saved it on every button press, it would
quickly wear out.

The scheme above would achieve this. Another is that such
configuration is only saved about a minute after it's set,
so if you power-cycle it too quickly, it won't be saved.

--
Andrew Gabriel
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