I have now found another problem. If I also enter a promotional price to the regular price, then the calculation is also not executed correctly.
With this example you can see it:
https://to-stoffe.jk-design.at/produkt/baumwollelasthan/
The regular price is €18.90 the promotion price is €9.50 for 1m
For 10cm, 20cm, 30cm…. no value is calculated at all and for +10cm, +20cm,… the value is too high.
This also does not work if I enter an offer price and then reduce it with, for example, 50%.