Feature/interval ratio 3digit precision

[bishibashiB]

HI!
Awesome add-on... using it a lot lately. ... here is a thing about I like to improve the interval settings.
Maybe you can kindly hint me to any test procedure to validate the PR~,

Itentions:

• 1st change I interpret there is a bug in the interval_ration option as - for odd number of tabs - is multiplied twice (also line 43,44)
• 2nd change: For me i had a total length of 18cm and wanted to have 7-8 tabs on it. limiting the ratio to 2 decimals did not allow me to get results in a accuracy of 0.2mm (1% of 18cm) which adds up to around 2mm after the 10th tab.

[luzpaz]

@bishibashiB you can click on the line number in the code and copy/paste the URL so it's more convenient to see the code you're referring to.

CC @execuc have you seen this PR?

[luzpaz]

Ping @execuc are you still maintaining this freecad workbench?

[luzpaz]

bump @execuc