I made a bubble chart in Excel but can't figure out how you show the user what the size of the bubble means!
The Y and X axes have labels but what about the size of the bubbles?
Update: as of now, it seems the answer is "you cannot", but if anyone thinks it is possible, please let me know how.
If you right-click on the chart, you will see an option for Chart Options. Most of these are also available as you walk thru the chart wizard. Personally, I would either add a label as the chart title or as one of the axis desriptions detailing what each point means.
There are some guidelines for using bubble charts here
It seems that most bubble charts are for financial data, so the correlation of the size of the bubble generally relates to the total % that the data point takes up in the series.
Turn on data labels (to show X or Y) then right click on the data label to "Format Data Labels..." Label options then appear that allow you to change what the label contains (i.e. change it to show bubble size)