This is a question that came up recently. My first thought was add a secondary axis, but in this case the small and large values were in the same series. I thought there might be something available as a third party add-in for Excel.
Solutions to Try
I did find an answer by Jon Peltier which looks good and gives step by step detail, but also appears to be a lot of work. This article provides links to alternative approaches at tushar-mehta.com and andypope.info – which has a zipped example to look at. If you are seriously into graphs you should visit Jon Peltier’s blog.
Third Party Add-ins
The next place I looked was at the Microsoft Downloads Marketplace and found a Chart category – but no search tool for this area – you will have to follow the links to the vendors site and read up on each one. A good search function is really needed here. I clicked through on a few and didn’t find any likely starters.
Did I mention Microsoft really need better search tools on the Microsoft Downloads Marketplace?