For years we pretty much mounted our scopes the old fashioned way, setting our rifle between two sandbags to level it out, placing the scope in the rings and using our eye to “level” the horizontal bar of the reticle and then adjusting the vertical component until it was perpendicular to the axis of the rifle.
While it worked, it was time consuming and not always perfect. Since that time, several inexpensive reticle leveling systems have come on the market that work well for the average shooter who mounts only one or two scopes a year.
However, for professionals who set up scopes for paying customers, a faster and more accurate system is required. Wheeler Engineering designed their Professional Reticle Leveling System with dealers and gunsmiths in mind (and folks like us who like neat time-saving tools).