There are jobs wherein you cannot say that a line is straight unless it is really straight. In some cases, even a slight bend in a line can affect the entirety of a design. That is why professionals never use book spines, random wood planks, or mobile phone edges to determine if a line is really straight. The tool that can accurately help you determine straight lines is a straightedge or a ruler. These perfectly straight bars are carefully manufactured to have undeviating edges for accurate reference. The ruler, aside from its straightness, also provides length markings useful for short length rangefinding.
AlumiColor 42" Non-Slip Steel Edge Straight Edge (Silver) - 1213-1
AlumiColor 48" Non-Slip Steel Edge Straight Edge (Silver) - 1214-1