Stringgrid checkbox Column show 'True' or 'False'

In a AdvStringGrid i have 3 Columns with Boolean Data and set a Checkbox in this Columns with: 

For i := 1 to grd.RowCount - 1 do
    for j := 1 to ColCountMax - 1 do
      Case j of
        7, 8, 9, 10, 12, 13:
          grd.Alignments[j, i] := taRightJustify;
        15, 16, 17:
            grd.Alignments[j, i] := taCenter;
  ===> grd.AddCheckBox(j, i, AQuery.FieldByName(GridFieldNames[j]).AsBoolean);
    AQuery.Next; // Nächste Zeile in DB

When Running the Programm then in the Grid there are not only the Checkboxes but also the Text 'True' or 'False' right of the checkbox.
Do you know this problem and what am i doing wrong here.

Add the checkbox as data checkbox (with last param true)

thank you for Help,
I have added a fourth parameter True and it has worked.
The explanation in the guide did not sufficiently explain to me what the 4th parameter is good for.

Unfortunately, only the display works but not the readout. I had previously worked with:

GetCheckBoxState(15, lRow, State);
RechRec.Erledigt := State;

but this no longer works, it always returns false from State.

Are grid.CheckTrue / grid.CheckFalse set to the values you have for true & false (Wahr / Falsch) ?

Yes thats it is.
I have to set grid.CheckTrue:='Wahr' and it works.