I posted recently about the very useful Dual function (to store a numeric value and a text value - e.g. for Months).
Another good application of this function is in a chart calculation. If your calculation includes a dual, e.g.:
Dual(Country & ' (' & Num(Sum(Sales)/Sum(Total Sales),'0.00%') & ')', Sum(Sales))
Then you will have both a Number and a Text value - either or both can be displayed on the chart using the "Text on Datapoint" and/or the "Numbers on Datapoint" options in the Express Tab of the chart.
One use of this is to display 2 disfferent calculations on, say, a pie chart. In the above example, the Pie chart could be set to display both the total values and the percentages - something that is not achievable any other way.