The fourth step, verify checksums, is included to verify checksums
of received GPS data. If the checksum is bad, that particular
string is discarded. The other data is not necessarily discarded.
For example, if 8 receivers sent data, but 2 checksums were bad,
the other 6 receivers’ data would still be processed and recorded.
The number of good data was recorded each time, so if the above
scenario happened, the custom GPS sentence we made would say
‘‘6” instead of ‘‘8”.