Most modern car audio amplifiers have a built in crossover on the side. Usually, it will start at 30hz and have a huge gap, all the way up to (sometimes) 500hz. The purpose of this tool is to enable the installer to set the crossover frequency of an electronic crossover to the desired frequency, accurately and quickly. Enter "Competition Mode" and easily match gains on any 4-channel amplifier or even multiple bass amplifiers. This is VERY important when using subwoofers that share a common chamber, especially if you have 2 (or more) amplifiers on a dual voice coil driver.