double length = PolishNumericFunctions.Round((double)treeLengthCol.Value, 2);
                treeLengthCol.Value = length;
                double convFactor = this.FindWoodConvFactorMS(artNr);

                double mp;
                if (mpCol.Value != DBNull.Value
                    && (widthCol.Value == DBNull.Value
                    || dmCol.Value == DBNull.Value))
                {
                    mp = (double)mpCol.Value;
                    dmCol.Value = DBNull.Value;
                    widthCol.Value = DBNull.Value;
                }
                else
                {
                    mp = length;
                    mp *= (double)widthCol.Value;
                    mp *= (int)dmCol.Value;
                    mp /= 100.0;
                }

                m3Col.Value = PolishNumericFunctions.Round(convFactor * mp
                    , 2);
                mpCol.Value = PolishNumericFunctions.Round(mp, 2);
                return true;