Answer:
Suppose the Proportional relationship bettween two variables x and y, is
y=mx
→Rate of Change that is unit Rate is equal to

Where, m=tan Ф,where Ф , is the angle made by line with positive direction of x axis.
So, if you have calculated unit rate of change, it will help you to draw the graph accurately, because you know the angle made by line with positive direction of x axis.