I have a requirement to create a combination of a step line chart and an area chart. My area chart looks like this:

But I need the edges of the areas to be vertical, not at an angle as they are. I understand this is because the chart is drawing the area between two samples of data. However, using the same record set with the step line chart I get the following result:

This is what I need, however I need the areas below the lines filled in like an area chart.

This is the record set I'm using:

Does anyone know how to achieve this? I can't find anything in the user manual or the settings that suggests how I might do this. Google's stepped area chart does it perfectly as shown below: