Thank you all. This tip is great!

Vin you're right about this:
PPS: it might be quicker to sum those fields all at once:
SUM importedd TO xImpDD, costounit TO xCostoUnit, costot TO xCosTot, costoumn TO xCostoUMN, costotmn TO xCosTotMN...

but the correct sintaxis would be

SUM value1, value2, value3 TO var1, var2, var3

The first sintaxis gave me an error message.