Is the Objective Grid formula support 100% Excel compatible?

No. Objective Grid formulas are similar to Excel and mostly compatible. However the formula are not 100% compatible.

Objective Grid provides many more worksheet functions that are not supported by excel. Examples are matrix operations, financial functions and many more.

On the other side Excel also has worksheet functions that are not supported by Objective Grid. Examples are the database functions in Excel.

When passing arguments to functions Objective Grid is not as advanced as in Excel 7. For example, if you pass a date string to a function that accepts only a date value you have to convert the string to a date value.

Example:

EOMONTH(DATEVALUE("7/7/93"), -24)