Kanon: Rule or Ruler?

          The biggest eye-opener of Dungan's book Constantine's Bible was the use of the word canon, or kanon, in antiquity versus the present. In antiquity, specifically in Greek Polis, canon was used "as a metaphor for accuracy, definiteness, and truth...[for the] sudden thirst for order, clarity, and accuracy" (14). In a society obsessed with mathematical calculations and predictions for everyday things, it was important to use accurate systems of measurement to ensure efficiency and precision. With that being said, the physical ruler that today is used in schools and businesses worldwide stems from the sticks used in antiquity for the same reason, measurement. Because of its accuracy and efficiency, the ruler became a metaphor by the name of kanon. For example, in Polis, there were guidebooks filled with instructions for building things, the majority of which were named Kanon of (insert product name here). 
         While it is understandable that kanon stood as a reference to a metaphor for a ruler in Polis, it is surprising that the ruler later came to stand for rule. Though ruler and rule are spelled similarly, the context in which they are used are very different. Dungan explains that as time continued, kanon came to stand for rule in terms of a list of guidelines or governing principles. It was brought to the readers attention that kanon went from metaphorically standing for ruler, a physical tool for measurement, to rule, an understood list of governing or important guidelines. The differences between the two meanings are exponential which makes me question the use of the word usage in modern cultural discourse. Are religious scholars referring to ruler or rule when they are discussing potential canonical texts? When looking at how kanon was used in antiquity, do scholars take into consideration the earlier meaning of the term or remain using the current definition for the term? Is there a definition of the term kanon?