It doesn't necessarily have to be a CAT scale . Flying J uses the J scale and some truck stops use Interstate but you must use a scale that gives 3 different axle readings . Driving on a single scale one axle at a time , subtracting the new reading from the previous to get the next axle weight will not give an accurate reading . I'm talking about a single scale long enough to weigh the whole rig . A small scale that weighs only one axle at a time is o.k. . A CAT scale costs about $5 but they charge less for a reweigh if you have to shift the load .