Description: Sal finds constant of proportionality by looking at the graph of a line. The following graph shows a proportional relationship. All right, now let's do this together, and let's remind ourselves what a constant of proportionality even is. If we know that there is a proportional relationship between y and x, then there will be a constant of proportionality between these variables, and what this is, is it is a number that I would have to multiply x by to get to y.*Teacher Advisor is 100% free.