Using a question mark (?) as the address character, causes the Levelogger to respond with the acknowledge active command (a!) where a represents the Levelogger address. A typical command/reply would be: ?!0<CR><LF>. The bold-faced characters are sent to the Levelogger; the normal type-face is the Levelogger's reply. In this case the Levelogger address is 0. You can only use (?!), the address query command to find out what the Levelogger's address is, if there are no other Leveloggers connected on the SDI-12 network.