> I dont even think it would play major role, measurement is done by correlation, moving closer/further only scales the picture. Scaling the picture is the pro

> I dont even think it would play major role, measurement is done by correlation, moving closer/further only scales the picture. Scaling the picture is the problem. What parent is trying to say is that the distance the physical paper has to move for the sensor to see 1 pixel of movement depends on the height of the sensor above the paper. If you want to know how many millimeters the paper moved based on sensor input, this is important (especially if you want precision on the order of dot size in high-dpi printing).