I've been told that at one time tuning was a little flatter than now, when it wasn't possible to measure it. When tuning from free-reed instruments, especially the concertina, it pays to be careful, as they flatten when played more loudly than usual, which is why Salvation Army concertinas were tuned slightly sharp. Mind you, I've also heard an enthusiastically played guitar that was so far out of tune that changing chord-shape made no real difference, it still sounded like a drum. He had some great songs, though. Chris.