Why do I get 0.00 for "" in a formula?

[Guest]

I get the correct (blank) response for this formula:
=IF(ISNUMBER(DAVERAGE(EXT_DAILY_DATA,EXT_AIM_ACHIEVED_CLAMPED_START,APR_CRITERIA)),DAVERAGE(EXT_DAILY_DATA,EXT_AIM_ACHIEVED_CLAMPED_START,APR_CRITERIA),"")

but I get an incorrect response (0.00) for a formula created the same way:
=IF(ISNUMBER(DAVERAGE(EXT_DAILY_DATA,EXT_TIME_IN_START,MAR_CRITERIA)),DAVERAGE(EXT_DAILY_DATA,EXT_TIME_IN_START,MAR_CRITERIA),"")

I have already checked the cell formatting and it is the same.

 

[T. Valko]

The only possible explanation is that the second formula is calculating an
average that equals 0. Excel would not mistakenly return a 0 for a blank.

Biff