Speaking as the owner, at various times and in various places of 10 an Eko Ranger 12; 2) an Ovation Celebrity 12 and now, (at last a good one!) - 3) a 29-year old Japanese-made Sigma 12 I can confidently say that tuning a 12 is neither easy nor pleasant.

The Sigma sounds great and doesn't go off-tune very easily, except if it is subjected to significant temperature changes. So I don't gig with it and it lives - on a stand - in the room I play it in the most.

Both the others would go out of tune if you looked at them sideways. The Ovation was the worst, possibly due to neck flexion, but if you played it long enough and tuned it between every song, it would eventually settle down. The Eko was good from the tuning point of view but was terribly heavy to play and not a very inspiring sound.

I very nearly gave up playing 12's altogether, but was tempted by the Sigma and I'm glad I fell! I think that a good-quality guitar should maintain tune. As to getting it there, I use a tuner for the lower four strings (D through bottom E) of the lower courses and then tune the octaves and the top four by ear. At least the Sigma holds the tune on the lowers no matter what you do on the octave strings, so it is fairly easy to get it all sounding nice.