Formulas must return sumething (Excel has no missing or empty cell
value). Anything other than a number or a #N/A will plot as zero.
Either write an event driven macro to add the formula only when the data
is available, or else use a formula like
=IF(INUMBER(dailyData),formula,#N/A)
as I suggested yesterday. You can use a conditional format to hide the
display of error values in the cells if the worsksheet appearance
bothers you.
Jerry