The leading zeros allow the receiver to prepare to accept the data. SS is the usual Start Sentinel of 11010. ES is the usual End Sentinel of 11111. The LRC is the Longitudinal Redundancy Check There are 10 terminating zeros.

To overcome the problem of transmitting data with 'F' characters that would be seen as a terminator (11111) the data is converted into ordinary numerical base 10 strings. See example below.

Suppose a card contains hex data as follows 00004567AF. This will be converted into 0004548527 Note that this string is always 10 digits long and is calculated as follows:-