Sorry, but now i have another problem.

I do this Class and i need pass to the second parameter of CAMBIA Procedure and return values width 8 dicimal places (like this number 0.00498798). How this is possible width the supported Crytal Report data types (Integer, Long, Single, Double, Currency, Date, Boolean and String).
One way is to change the data type of nTaxa and Return Value to String Type, is this the only way?

DEFINE CLASS Global AS CUSTOM OLEPUBLIC

PROCEDURE Cambia( nValor as Double, nTaxa AS Double, nRound AS Single) AS Double

IF nTaxa > 1
RETURN ROUND( nValor*nTaxa, nRound )
ENDIF

IF nTaxa <> 0 AND nTaxa < 1
RETURN ROUND( nValor/nTaxa, nRound )
ENDIF

RETURN ROUND( nValor, nRound )
ENDPROC

ENDDEFINE