The treadwear grade of a tire is a comparative rating based on the wear of a tire when tested carefully under controlled conditions. For example, a tire graded 400 should have its useful tread last twice as long as a tire graded 200. However, a different tire manufacturer may grade a comparable design as 300, so a grade of 150 would last half as long under their grading scheme. Therefore, it is not recommended to use one manufacturer's grade versus another, but instead to compare tire grades within a given brand. Actual treadwear performance can vary tremendously according to the tire's real-world use. Variations in driving habits, service practices (especially air pressure maintenance), road conditions and climate will affect the life of treadwear.