Running a cord INTO Your headphone jack will do nothing [if you are lucky] as it is a {high impedance usually} output jack. Only put suitable INPUT sources into INPUT Jacks -only put out to a suitable source (ie running your 8ohm amp to a 4ohm cabinet can overload the components) and connecting straight from your headphone jack to another amp could feed it too much voltage.
Accuracy,you say? hmm interesting concept..