The problem may be how the bookmark was created.  When a bookmarked cell is used in a formula, the initial results may be accurate.  However, once the formula is recalculated the results change and are inaccurate.  It is important that bookmarks used in formulas are for the contents of an individual cell, and not the cell itself.   We recommend that you use the Formula Builder Wizard to create the bookmark, and then add the bookmark to the formula by double-clicking the bookmark name in the left panel of the Wizard.  Bookmarks created using the Formula Builder Wizard ensure that only the cell contents are bookmarked.