I've been designing panels and decals in Photoshop for the past couple months and something I've noticted while doing so is whenever I set sometime to a certain dimension, Photoshop will add to those dimensions. For example. I want the canvas to be 111mm x 61mm. I put that in the box and press enter. But now, the canvas is 111.12mm x 61.03 mm. Why is that? This could be another issue but that also might affect the fact that when I print said decal, the demensions are not what I put in the box and certainly not 100% scaled. They are always off.
That still doesn't work for me. Setting the the image size to 61mm x 111mm and setting the resoultion to 300 ppc or 120 ppc, and the scaling to 100% the printout is actually 107mm x 59.5mm. It could be an issue with my method of printing.