A piano or tuner is the best way to insure that your intonation will not improve. The well tempered intonation of a piano is a comprimise to be able to play in every key. The piano player cannot adjust single notes on the fly. Relative means just that. Each tone needs a "relation" to another. That means that the pitch of a note like an E is different depending if I am playing in the key of C, E, A......... I think it is important to get two players together and have them play different notes and LEARN that when they are in tune with one another that resonance gives us the confirmation.