tricky data entry question
 

I need to limit a cell's entries to numbers, commas and dashes, so
entries such as 1,2,3,4-10,17 could be entered (these are just
examples, the actual figures can go up to 999999).

The tricky part is that I would also like to only allow an entry in
this cell if another cell on the sheet is not empty.

An example to summarise: I want to be able to say "allow an entry in
this cell if cell A1 is not empty, and only allow the characters to be
numbers, dashes or commas."

Of course it may not be data validation that I need, (maybe a
combination of number formatting and data vlidation?) so any
suggestions most welcome.

I would like to avoid macros, as this is going to be handed over to a
user, and if she changes the spreadsheet I don't want her to have to
change macros.


TIA

Steve