Demand - Supply curve... with "steps"

Hi,

I am trying to remake a supply-demand graph from a report, but I have some problems getting the right layout.

The supply curve in the example is not liniar, but is build by 'steps' (the graph I am trying to remake is included in attached excel file).

I have problems with the vertical lines when going from one 'step' to another.

I hope you understand and are able to help me

Thanks in advance,
UnigeekMerit order effect - Supply and Demand.xlsx

You need to construct the steps.
This has various methods
http://www.andypope.info/charts/stepchart.htm