When enabling a monitor, there is no physical size information

[ralsina]

To reproduce:

• Start with a disabled monitor
• Enable it
• Try to set it to scale to physical size

It fails with an error, because when xrandr info was collected, the physical size information is missing.

[ralsina]

In some cases (laptop monitors) we can get this via xrandr --verbose + EDID even if it's turned off.

[ralsina]

Getting it via xrandr --verbose + EDID works for anything that is connected. If it's not, then it doesn't work (which makes sense)

[sirtaj]

Bear in mind that some monitors straight up tell lies about physical size. I've had one monitor that reported itself as a 7" diagonal for some reason.

[ralsina]

Nowadays most monitors seem to be fairly honest, although there is already a case of a monitor reporting to be smaller than it really is. The "scale so windows are the same physical size across monitors" is a bit of a gimmick anyway ;-)