**How to calculate (by hand) the slope of a line in a graph: **

**(Note- In experiments using Excel functions, the slope is
not to be determined using this method: it must be determined using Excel. See Prelab
11)**

Pick two points (X-value, Y-value) that are ** on the line.** The easiest
points to pick are points where the line crosses the grid of the graph paper so
you don't have to extrapolate the x and y values of the points. In this
example, Point 1 could be (5,10), i.e., X_{1} = 5 and Y_{1}
= 10, and Point 2 could be (10,20), i.e., X_{2} = 10 and Y_{2} =
20.

Plug these two points into the following formula to calculate the slope: