This giant level provides visual leveling assistance from the driver's seat. It helps calculate how much blocking you will need, with 1 mark on the level equal to 1" of blocking In addition to the side-to-side level, there is a second front-to-rear level that can be easily viewed while operating your tongue jack. Aluminum base is 11" wide. 2-3/4" high. Easy to install with four screws or rivets.