Official Luthiers Forum!

No affiliation.
Maybe someone in UK could use one?
Aluminium, aircraft grade, £29.99, 965mm, flat to within 0.04mm over its entire length.
Checked mine and it's inside that spec.
https://www.rutlands.com/sp+measuring-rules-straight-edges-precision-aluminium-straight-edge-with-metric-scale-965mm-rutlands+r9031?utm_campaign=Googlebase&utm_medium=organic&utm_source=Googlebase&geoip=GB&gclid=CjwKCAjwjuqDBhAGEiwAdX2cjzqbMUaOF2MLaqPlMpmXB98gv9GxNk_O0FUmDssdllrAw8s6QN8aABoCY-YQAvD_BwE#nogo

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I recently bought a new straightedge based on a recommendation by someone here but forgot who. It is a near copy of the straightedge I bought as the first tool specific for guitar repair, back a few years ago. It is a steel, imperial inch graduated, 18" long machinists rule that is about .1 " thick so it will stand on edge on frets. This company sells blemished seconds on the bay. I have bought two and the blemishes are minor and cosmetic.

https://www.ebay.com/itm/Blem-Cosmetic-Second-PEC-18-4R-Combination-Square-Blade-fits-Starrett-Mitutoyo/151441107417