Cool. This is actually really useful - I'm building a document editor at the moment. I think having the option for real-world size would be a nice feature.

I've been busy measuring different document editors with a screenshot of the ruler and it seems they all have different interpretations of A4 width (210 mm) at 100% on a Macbook Pro 16in:

- Apple Pages shows about 118mm

- Google docs shows 160mm in Safari

- Linearity Curve gives about 200mm