"the usual way of tuning a twelve-string was to tune the other eleven strings to the one that was out of tune"

Can't resist the opportunity to firstly repeat an old friend's comment about hammered dulcimers -
Q: How long does it take to tune a hammered dulcimer?
A: Research is continuing.

and secondly repeat his suggestion of a last request if he was about to be executed - a 12-string guitar and time to tune it.