[RESOLVED] Obtain Form Size in Millimeters

[passel]

What you get on the screen should rarely be a true size in millimeters, but rather a logical size in millimeters, since the physical dimensions of the screen itself can differ. For instance, I have a 1920x1080 screen that is 24 inches, and another screen that is also 1920x1080 resolution, but is 42 inches. The one signal is feeding both the 24 inch screen and the 42 inch screen. The size of the form can't visually be the same size in millimeters obviously.
And if I was using a projector, the physical size of the image would depend on the distance the projector was from the projection, so the size in millimeters would differ.

Even the logical millimeters conversion will be different depending on the DPI setting you have Windows set to, which doesn't have to match the true dpi of the monitor you're using. In your particular case, it could be a matter of your having the Display Properties "Size of text, ..." set to 125% as the difference between 81 and 100 millimeters is close to that scale difference.