Checking MsflexGrid Cells Contents To Ensure Not Null/Blank

Hello,

I know I must be annoying, anyhow I'm stuck.

I'm allowing the user to edit the MSflexgrid, however they are also able
to leave the cell blank with no contents. Not a good thing. Ugh.
It gets messy since when the user presses a button to do calc on the form it can't be done since the cell contains no value.
Should a check also be done in calc button area just prior to do the calculations?


Anyhow so I need to do a check to make sure that when the user leaves
the edit grid cell that the cell has an numeric value in it and that it is not
blank. Also I need it to do it for an unknown number of rows and only for certain columns ( not col 10- 13 and 16).

So any ideas, hints, examples..etc. on how to do this and where would be great.

Thanks