Use Half Cross Backward 
to place and erase the backward half of a full cross 
. Use single-click to place or erase one at a time, or drag to draw continuously.
Note: If part of a cross is replaced or erased, a half cross forward is left in the other part.
To Place a Half Cross Backward
-
Select Half Cross Backward
in the Create window 
, then click or drag on the work area to draw or replace crosses.
Note: Select Erase 
or press the Option key when drawing to erase crosses.