www.catscale.com has a video on how to use the scales. Also will show you where the scales are. Where we live, there are several truck stops near us. We learned that you must reweigh at the same scale or you will need to buy a new ticket. That said, if using the same scale, cat scale is usually $10-12 for first weigh and $1 for each reweigh in a 24 hrs period. When you pull up and push the button (bring a long handled scraper or broom stick because the button is high up), they will ask you for 1st weigh or Reweigh. Tell them first weigh and then they will ask for a truck number. Tell them private vehicle or private RV. Pull ahead, park, pay and collect ticket. There is a number on the ticket. Tell them reweigh, then give them the ticket #.
If you are too far from a cat scale, many local dumps have a scale and so do local feed supply stores. You may be able to use these but it is more difficult as they are typically a single scale so you have to pull each axle on individually to get your answers. Some states also allow you to drive over the scales and check your numbers on the state weigh station if they are closed.