Architects' and Engineers' Scale (the physical instrument)
	An architect’s scale is a specialized ruler designed to facilitate the drafting and measuring of architectural drawings, such as floor plans and orthographic projections. It is typically multi-sided (three lobes in cross-section) and features multiple units of length and proportional length increments.
Part of	Drafting Board
Part Type	Entity
Screenshot

This is an architects' scale. It is not to be used as a straight-edge (for cutting), but rather only as an instrument to aid in producing drawings at scale .

When drafting architectural scaled drawings, the architect's scale is not used as a straight edge - it is only used to mark specific measurements. Over time and frequent use, scales can gather dents or have uneven edges, leaving drawings looking unprofessional if used as a straight drawing edge. Instead, use the parallel rule or a T-square and a set of drawing triangles to put lines onto the paper. This will maintain a consistent parallel line across your drawings.

Resources

Reading Architects' Scales

A video on how to read architect's scales found on manufacturinget.org, and by developed by R. Hewitt at the University of Memphis.