Most states have weights and measures departments that certify all of the tools used in commerce (scales, gas pumps, taxi meters, etc). These tools are very hi

Most states have weights and measures departments that certify all of the tools used in commerce (scales, gas pumps, taxi meters, etc). These tools are very highly regulated -- often the internals are inspected by state officials, the devices are sealed, and operators are required to bring them back in for periodic re-testing. This may seem obstructionist, but it's based on a long history of dishonest merchants tampering with this type of equipment to defraud customers.