IConditionalFormatValuesRule.Formula Property
The formula to be evaluated. The conditional format will be displayed when it evaluates to true or a non zero value. If the formula equals to 0 or false, the conditional format won't be shown. Note that from Excel you can't set a formula, it will always be empty for databars, iconsets or colorscales. But if you set a formula in the xlsx file, it will be used by Excel and preserved when saved, even if Excel won't display it.
Note that with relative references, we always consider "A1" to be the cell where the format is. This means that the formula: "=$A$1 + A1" when evaluated in Cell B8, will read "=$A$1 + B8". To provide a negative offset, you need to wrap the formula. For example "=A1048575" will evaluate to B7 when evaluated in B8.
Syntax
Unit: FlexCel.Core
property IConditionalFormatValuesRule.Formula: string