Thanks for the response.
I've managed to do a combination bar & line chart as you suggested and it works fairly well. Hopefully the client will be satisfied with it.
Now I have another question which I've been wondering about for a while.
QUESTION: Is it possible to force the Y axis labels to display a particular value?
For example, if I've got values ranging from -50 to +50, can I force the graph to always show zero? Right now I've got graphs like that and depending on the particular number of datapoints and the particular values of those datapoints, some of them show zero and some of them don't.
For consistency of representation I'd like to be able to ALWAYS show zero.
Hoping for a positive response to this one :-)