said by CarlaBoots :
I was thinking about something that I can install on my PC
They don't. The problem with that though is SL has already come out and said that their meter is what will be used for all their purposes and that your meter could be wrong. Plus, if the SL meter doesn't update on time, that entire days usage gets zero'd out and there will be a larger difference between you and them.
If you are wanting something just as a quick visual reference though, there are numerous third party programs, both free and paid, that will count traffic. Many routers also have built in meters, you just have to set them up and turn them on.--
50/3 Suddenlink : Current
5/1 CMA : Old
15/2 TWC : Old