Moving truck weight question

[NPloysa]

Saw an Atlas Van Lines truck on the way home as he was getting into the weigh station lane. On the truck's (KW T2000) molded fairings over the fuel tanks, it read "TARE 18500 AT 6999".



I know it has to do with the tare weight, but what exactly? And does the "AT" mean "at 6999" or "AT" as an abbreviation?



Thanks!



Nick