Progress bar charts compare two series' values: they show how much one series values are, compared with another series. Last background series bars are always at 100%, while the front series bars show the percent of their values, compared with the back series. Such charts may also show the fraction a series action was completed, compared to another series.
Our UK vs US Sales Progress demo charts show the percent of UK sales (as product quantities), compared to the US sales (always at 100%), in the same three different years: 2007, 2008 and 2009. The multiple series are the US and UK countries. Remark the vertical X axis is a category axis: year values are distributed at equal intervals on the axis. Quantity value bars for each year are displayed one within the other for each country, with a containment visual effect. It's like each US bar contains a UK bar. All bars for a specific country have a different distinct color: US bars use the first palette color, and UK bars the second palette color.