Let's say for example that w = 10 and q = 7. This means the distance between these values is w-q = 10-7 = 3. This is the distance between w and q.
Now let's make q larger. If w = 12 and q = 20, then w-q = 12-20 = -8 assuming we subtract in the same order. We use absolute value bars to ensure the result is positive. So instead we say
