The PICKADD System Variable determines whether subsequent entity selections add the entities to the current selection or replace them.

The values / options for this variable are:

0- Adding entities is turned off. The most recently selected entities replace the previous selection and become the selection set.

1- Adding entities is turned on. The most recently selected entities are added to the selection set.

2- Adding entities is turned on. The most recently selected entities are added to the selection set. If you used the Select command, entities remain selected after the command ends.

Note: When the replace mode is active (0), press Shift during selection to add entities to the selection. When the add mode is active (1 | 2), press Shift during selection to remove entities from the selection.

As for any System Variable to check/change the System Variable, Type the System Variable in the command line, and Press Enter.