Question 879287
<pre>
{{{drawing(400,7200/13,-3,10,-5,13, 
grid(1),
graph(400,7200/13,-3,10,-5,13), 


circle(7,10,0.15),circle(7,10,0.13),circle(7,10,0.11),circle(7,10,0.09),circle(7,10,0.07),circle(7,10,0.05),circle(7,10,0.03),circle(7,10,0.01),

circle(7,-2,0.15),circle(7,-2,0.13),circle(7,-2,0.11),circle(7,-2,0.09),circle(7,-2,0.07),circle(7,-2,0.05),circle(7,-2,0.03),circle(7,-2,0.01)

)}}}

The upper black dot is at (7,10) 
The lower black dot is at (7,-2) 

The upper black dot at (7,10) must fall twelve units to be where the
lower black dot is.  A fall of twelve units is indicated by -12.

Here's how to get that

end point's y-coordinate, -2, minus beginning point's y-coordiate, +10,

(-2)-(10) = -2-10 = -12 

The change in the y coordinate is -12.

Edwin