Hi,
I think try with format
&field(.<nat.number>)& Limits output of decimal places to <nat.number>
Display values like &WA-MENGE6(.2)& that should limit it to 2 decimals.
Help Link
http://help.sap.com/erp2005_ehp_04/helpdata/en/1c/f40c6fddf311d3b574006094192fe3/content.htm
Cheers,
Arindam