Mean Mother tyre gauges are shock resistant, reliable, easy to read and operate. They have ANSI (American National Standards Institute) grade B accuracy. All of our Mean Mother gauges have been tested to ANSI standards for their precision and accuracy. The classifications relate to the scale of the gauge. The scale of the gauge, commonly referred to as the pressure range is divided into three equal portions when characterising its accuracy. For example 0-20psi, 20-40psi and 40-60psi portions of the dial. Mean Mother gauges have a Grade B accuracy, meaning the accuracy for the 0-20psi and 40-60psi portions fall to within 3% of the actual pressure being measured.