anchor.diff:      'End Date'
     ];
   
  +
     /// Waits for Office APIs to be ready and then creates
     /// a new spreadsheet with [sheetName] and populates the spreadsheet with
     /// entries in the [insertionOrderList].
  
positive.code:       // This formula calculates:
        // (spent / budget) / (current duration / flight duration)
        //
        // Flight duration is calculated by (end date - start date + 1), and
        // current duration is calculated by (now - start date + 1), so it is
        // guaranteed that divide by zero will not happen.
        /// TODO: calculate difference at hours level if it is shorter than a day.
        /// Issue: https://github.com/googleinterns/dv360-excel-plugin/issues/57
        final formula = ''' 
         ($_spentColumn/$_budgetColumn) / 
         (
           (DATEDIF($_startDateColumn, NOW(), "D") + 1) /
           (DATEDIF($_startDateColumn, $_endDateColumn, "D") + 1)
         ) < $_thresholdAddress
        ''';
  
        // remove all tabs, newlines, and whitespace from the formula.
  
negative.code:       Util.convertMicrosToStandardUnitString(
            Int64.parseInt(budgetAmountMicros));
  
    /// Converts proto [Date] into Excel date time format.
    static String _calculateDate(
            InsertionOrder_Budget_BudgetSegment_DateRange_Date date) =>
        '${date.month}/${date.day}/${date.year} $_timeFormat';
  }
  
  /// Below are wrapper functions for Office Excel APIs.
  