Shinwa 12" Aluminum Cutting Ruler with non-slip back
This aluminum cutting rule from Shinwa has an edge that is designed to be used as both a low cost 12" ruler and also to function as an edge to use a knife against when cutting veneer, paper, leather or other thin materials. It is wider (35mm) than a typical ruler so that fingers can be kept away from the cutting and there is a non slip pad on the backside to help prevent movement when cutting or drawing a line.
The straightness tolerance is better than ±0.3 mm (0.012") over the length of the cutting edge. The aluminum is stiff enough to be used for cutting, however is softer than cutting knife, so won't damage the cutting edge if they accidentally contact.