This is anexcellent tool, it allows you to set gains and find your max head unit volume in minutes. It took me 30 lazy minutes (most of which was pulling amps and hu out) to set my brothers hu and 2 amps. This is a must have for anyone that s installing a system. It comes with a test tone cd, manual, probes and unit. Like I said in another post the brains behind the Rockford Fosgate T15k (15,000w amp) designed and built this product. This isnt some fly by night rookie Tony D'Amore is GENIUS and him nor steve would put their name on anything less than top notch.