Keltic harp tuning when no key is available

This is probably a very very rare issue that needed a special solution. Anyway. If somebody out there find him or herself in the same situation, read on, remember, and know what to do.

If you’re out on a stage, with a folk-band, you have your basic tools, the harp is seriously in need of tuning, but, alas, no tuning key can be found, do this: