It may be so that GLS215 shows debit (D) or credit sign (C), which makes it more difficult to calculate when you copy/paste values into excel.

GLS215 allows to change the debit / credit sign.

Go to actions and select F16 – change debit/credit sign..

Now GLS215 shows just negative and positive values.

Now you can copy to clipboard and paste in excel

Now excel can calculate values as to be expected.