Using a meter to check tint shade percentage is the only way to truly know what percent the tint on your car really is. One big and costly mistake some shops make is by eyeballing or guessing the percentage. Just because the installer applies 35% to the glass does not mean it will meter out at 35%. All windows have a die inside from the start. So if you apply a 35% film to a window with a 5-8% die inside already, you end up with 30-27% when checked with a meter. Here in Missouri the law is 35% for the driver and passenger front windows. Unfortunately in most cases
the exact percentage is only know when you are being given a ticket by a police officer who has a meter.
To make sure you are within state guide lines for window tinting, ask the shop if they have a meter to check the percentage.