Scaling Calculators

Text file: HTML code that ive commented most of it, save it as a .HTML file to open it in the browser.
Executable: Not uploaded due to TVerse not allowing this format. Instructions are at the end on how to make it.
PS1: Powershell script that can be edited with a text editor, looks cool, no frills.
STL: Only there so this thing gets published, just a placeholder.
PDF: 4x Grey dots and faint yellow on the LH RHC of an A4 page, for 10cm and 4in, as a test print before you print the real doc to not waste a page.

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Often I find I need to resize a second print that I find doesn't quite match in size to where it is going.
Say for example I have a functional print that I want glued onto a real life object, and once I print a test print I find its a little off in one or more axis.
This could be for various reasons,
Printer E steps aren't calibrated
My initial measurements were off
I CBA to redesign it in CAD
Im loo