POSTNET
...that the U.S. Postal Service's POSTNET uses a checksum to verify zip codes?
...that the <a href="./United_States_Postal_Service" id="mwhg" rel="mw:WikiLink" title="United States Postal Service">U.S. Postal Service</a>'s <b id="mwhw"><a href="./POSTNET" id="mwiA" rel="mw:WikiLink" title="POSTNET">POSTNET</a></b> uses a <a href="./Checksum" id="mwiQ" rel="mw:WikiLink" title="Checksum">checksum</a> to verify <a class="mw-redirect" href="./Zip_code" id="mwig" rel="mw:WikiLink" title="Zip code">zip codes</a>?