When defiing the data set for chart, it can not handle a data set
if it is not a continuous range of a column (or row).

In scientific applications it is often the case that a data set
to be charted is actually a concatenation of blocks of data that
are located at distant places on the spreadsheet. For example,
if you have an experiment that runs for weeks, you may up with
starting a new column for each parameter at each week.

If then you want to create a chart that shows 2 parameters for the
entire experiment, you can't - the data sets are physically not a
continuous block of data.

Both Excel'97 and ApplixWare 4.2 can handle data sets where the
data is a collection of cell ranges or even individual cells.

I attach an Excel'97 spreadsheet, with a chart. The chart should
show 2 data sets, one increasing and the other decreasing. Importing
to OOo, it will show only one data set, a concatenation of all the
two sets.