The watermark won't appear on final print. All sizes are in inches (1 in=2.54 cm).
Important! If you're on a wide-gamut monitor make sure to set your colour profile (ICC-profile) for web to sRGB otherwise the colours are fully stretched and my photos look oversaturated which they are not.
The only other solution for wide-gamut monitors is to use Firefox and set the gfx.color_management.mode to 1. Type about:config, press enter and do as advised.
So far no other browsers provide colour management. Correct me if I'm wrong.