Creating a total cost chart where a component cost is a step cost
 

Hi, I've referred to Andy's step charts at
http://www.andypope.info/charts/stepchart.htm where he duplicates x values in
order to create sharp straight steps in an XY scatter diagram.

However, I don't want to duplicate x values. Rather, I created a dataset as
follows
Volume Step Cost
0 0
1 20
100 20
101 40
200 40
201 60
300 60
301 80
and the pattern continues to 4000.

The XY scatter diagram chart that is created is incorrect. The chart line
steps up from 0 to a y value of 20 at x=1, stays flat to x=100, then climbs
as a diagonally straight line to the y value corresponding to x=1000, at 1001
it steps up by an increment of 20, then stays flat to x=1100, then climbs
diagonally up as a straight line to the y value corresponding to x=2000, and
the pattern continues. Weird!!

Especially weird is the fact there are discontinuities in the line at x=1,
100, 1000, 1100, 2000, 2100, 3000, 3100 etc but not at x=200, 300 etc thru to
900, 1200,1300,1400 thru to 1900, 2200, 2300, thru to 2900, etc etc.

I need to add this step cost data with other cost types so as to graph total
cost. Therefore manipulating the data in order to create the correct picture
is not an option ... I want Excel to "do it right". Any ideas why this is
going wrong please? I'm using Excel 2007.
TIA .... Greg