Help with chart referencing a pivot - Mac vs PC issues

Hi,

I have these charts that need to be updated. The pivot gets updated with a new data column for the previous days data so in this case I want to add the data for 12/20. I'm having a strange issue where on a mac, I can just click on the chart and drag over the boxes to add the next day, and the charts update with no issues. However, on a PC when I try that the axis get switched around and messes up the chart. Excel 2007 is used on both machines. Why is this happening? Data for the new day will be added every day, is there a way to automatically update the charts?

Thanks!