AbstractCalculationMonitor class

Monitor for user to track the progress of formula calculation.

The AbstractCalculationMonitor type exposes the following members:

Property	Description
original_value	Gets the old value of the calculated cell. Should be used only in `AbstractCalculationMonitor.before_calculate` and `AbstractCalculationMonitor.after_calculate`.
value_changed	Whether the cell’s value has been changed after the calculation. Should be used only in `AbstractCalculationMonitor.after_calculate`.
calculated_value	Gets the newly calculated value of the cell. Should be used only in `AbstractCalculationMonitor.after_calculate`.

Method	Description
`before_calculate(self, sheet_index, row_index, col_index)`	Implement this method to do business before calculating one cell.
`after_calculate(self, sheet_index, row_index, col_index)`	Implement this method to do business after one cell has been calculated.
`on_circular(self, circular_cells_data)`	Implement this method to do business when calculating formulas with circular references.