Well, that procedure was the only appropriate way of aligning a real life ruler with photo size. So now, whatever size photo i create, i know that i have to set the resolution to 37 pixels per cm in order for the photo to look real on my Dell 2407WFP monitor.
I just thought that there is a preset in Photoshop to automatically select my monitors profile. I mean ~ i see presets like A4, B5, NTSC and other stuff, but it would be nice that Photoshop CS2 had my monitors preset, so that it would not ask about pixels per square cm, and know that on my monitor one square cm has 37 pixels...
But yes, thank you for the answer...