If the comparison is between a cell value and two values, this is the minimum value; otherwise this is is the formula to be evaluated for the condition.

public System.String Formula1{ get; set; }
Public Property Formula1() As String

If the value of Condition.ComparisonType is a comparison between a cell value and a single value (e.g., Condition.Comparison.CellValueEqualTo), Formula1 sets or returns a formula whose result will be compared with each cell value in the set of conditionally formatted cells.

If Condition.ComparisonType is a comparison between a cell value and two values (e.g., Condition.Comparison.CellValueBetween), Formula1 sets or returns a formula whose result will be the minimum comparison value.

If the value of Condition.ComparisonType is Condition.Comparison.FormulaEvaluation, Formula1 sets or returns a formula that evaluates to true or false.

          ExcelApplication xla = new ExcelApplication();
          Workbook wb = xla.Create();
          ConditionalFormat condFmt = wb.CreateConditionalFormat();
          Condition cond =
               condFmt.CreateCondition(
               Condition.Comparison.CellValueGreaterThan,
               "=100");
          cond.Formula1 = "=99";
        
          Dim xla As New ExcelApplication()
          Dim wb As Workbook = xla.Create()
          Dim condFmt As ConditionalFormat = wb.CreateConditionalFormat()
          Dim cond As Condition = _
               condFmt.CreateCondition( _
               Condition.Comparison.CellValueGreaterThan, _
               "=100")
          cond.Formula1 = "=99"