Incompatibility with siunitx v3

[sieversMartin]

The class makes use of some features not available in v3 of siunitx. This leads to some errors, and warnungs, e.g:

! Undefined control sequence.
<argument> \SendSettingsToPgf 
...

Package siunitx Warning: Option "round-integer-to-decimal" has been removed in
(siunitx)                this release.

Package siunitx Info: Option "group-digits = true" has been deprecated in this
(siunitx)             release.
(siunitx)             
(siunitx)             Use "group-digits = all" as a replacement.

A straightforward fix (or at least a workaround) is to load the old version with \RequirePackage{siunitx}[=v2]

[krono]

This is true and probably I should have anticipated that…
Maybe a guard via latexrelease is in oder.

A workaround is passing the option before \documentclass…

[krono]

what is the best way to detect the presence of v3 before loading the file?

[sieversMartin]

What about \@ifpackagelater{siunitx}{2021-04-17}{\RequirePackage{siuntix}[=v2]}{\RequirePackage{siunitx}}.

2021-04-17 is the release date of the last v2 version.

However, according to the documentation, loading the package with [=v2] should work for all installations:

This approach will work with older systems which still have version 2 installed, mean-
ing that you can reliably use it to work between systems with different versions of
siunitx.

[krono]

The first won't work because (to my knowledge) this only works after loading a package.

The second is quite interesting!

[krono]

FWIW, Fixing the errors and using the ifpackagelater-variant is the better way…