dmm will be good but u gota know how to use it the right way . I would say u need to look at the amp and if its a off name company then u know its not gona put out what it says it will. Im not sayin that the big name companys dont lie a tad but its more then likely gona be the sh ity amps that are way off. You have to look at what the amp does at what volt thats so important now adays. if u can keep your volts up then your gona see alot more power.