I believe the line:

@draw.rectangle( i, @canvas.rows,
            i + step - 2, @canvas.rows - ( (r / @maximum_size) * @canvas.rows) )


should be coded:

@draw.rectangle( i, @canvas.rows,
            i + step - 2, @canvas.rows - ( (r / 100) * @canvas.rows) )

r values in this case are on a scale of 0-100, so dividing by maximum size (an arbitrary number) can cause incorrect
image display.