This command is used to ensure that a Levelogger is responding to the SDI-12 datalogger. A typical command/reply would be: 0!0<CR><LF> where the 0s represent the Levelogger address and <CR> represents a carriage return (Hex 0D) and <LF> represents a line feed (Hex 0A). All replies from SDI-12 Leveloggers are terminated with <CR><LF>. All datalogger commands are terminated with an exclamation mark ! character.