The 4/09 Shingle Gauge™ measures the thickness of a shingle, and based on analyses made by Haag, correlates that thickness to a warranty level. Knowing a warranty level can be important in determining what a comparable replacement shingle might be. While the Shingle Gauge™ was designed with the strictest analytical tolerances possible, we still consider it an estimating tool due to a small number of shingles which do not conform to the gauge. Haag created the 4/09 Shingle Gauge™ by testing asphalt-based composition shingles. Modified asphalt shingles (commonly called “impact resistant”) were not included in our testing and are not applicable to the 4/09 Shingle Gauge™.