Scan your gasket. Then you can bring the image into MoI and have a good ref for 50mm….

I also have these. They measure pixels, but you can measure known values then translate the values to calibrate your current display zoom…

https://www.iconico.com/caliper

I found Its kinof an odd attempt though. I think accepting that your screen is a digital representation and you can just trust MoI to give you accurate output is best

I ended up getting a Mitutoyo and other methods for real world measurements and just entering values. I was overthinking it….