CAT Scales are a widely used network of certified scales, usually found at truck stops, where a driver can weigh their truck and trailer for a small fee. Weighing before hitting the road lets a driver catch an overweight or unevenly loaded rig on their own terms.
A driver gets back a scale ticket showing the weight on each axle group, and can then shift the load or the tandems if any group is over its axle rating. It’s a way to avoid fines and failed inspections at an official weigh station.