When formalising diagrammatic systems, it is quite common to situate diagrams in the real plane, R2. However this is not necessarily sound unless the link between formal and physical diagrams is examined. We explore some issues relating to this, and potential mistakes that can arise. This demonstrates that the effects of drawing resolution and the limits of perception can change the meaning of a diagram in surprising ways. These effects should therefore be taken into account when giving formalisations based on R2.