On 14 Apr 2021, Robin wrote

On 14/04/2021 09:58, Clive Arthur wrote:
On 13/04/2021 22:01, Theo wrote:
Fredxx wrote:
Just keep an eye out for any changes.

There might be something you can do in terms of fixing some
cheap laser pointers (firmly) to the structure, and marking out
where the beams land. Then go at different times of day and see
if there's any difference. (turning them off when not in use,
obviously!)

(I'm not sure laser pointers are collimated enough, but worth a
try before
going for anything fancier)

Theo


If you have any small cracks, glueing microscope slides across
them is a good way to check for movement.Â* You can pick up a
pack of these on eBay for notalot.


With something so important I'd prefer a measure which avoids the
false alarm of a glass slide broken without developing movement -
eg

https://www.sccssurvey.co.uk/crack-m...-crack-monitor.
html

+1
(I've just posted a similar comment -- I should've read ahead....)

Cheers,
Harvey