need calculation that considers a blank cell to be '100'

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Hi,

I have a spreadsheet that counts the SVL achieved in intervals throughout the day. The data from rows 4-72 are pasted in from another system. My calculation in J3 ignores cells that are blank, however, I would prefer to consider a blank cell to be '100' as intervals with no data are bringing down our results. Does anyone know how I can do that within cell J3 without the need to manipulate the data in the rows below?

The document is 2003 compatible but I can make it a 2010 doc if that gives more flexibility.

Thanks in advance