Rulers and dividers are both tools that enable the discovery and definition of distances. While similar in their capabilities, however, there is a fundamental difference in the nature of the two tools. A ruler may be used to specify distances according to standardized systems of measurement (for example, inches or millimetres), whereas dividers are used to define proportional relationships. This paper compares the techniques associated with the two tools, in an approach that draws on the theory of extended mind (the idea that cognition is distributed across both people and things) to demonstrate how we might better understand the ways techniques can steer, support, or potentially compromise processes of design.