The Access PIN Code is the employee's login for POS devices: on the POS the staff member enters only the PIN and Sprwt matches it against active employees. Only employees whose Is Active? is on and whose user account is not suspended can sign in this way. The PIN is stored securely (hashed) and is never displayed again, which is why the field shows "Leave blank to keep current" when editing. To change it, type a new PIN and save.