Quantity mask

Hello...

In a editable field on ALV I can insert a quantity of PO item... The filed mas is X,XXX (in ALV).

I use the method ref_grid->check_changed_data to come back the informations of ALV report. But, when the quantity back the SAP change the number...

Follows a example:

In the ALV report: 1,000 (default mask)

In ABAP after method: 0,001

How Can I change this configuration?