Just don't use a guitar tuner. Or a piano. Your open C won't be C, it will be 440 * pow(sqrt(2,12),7) which is ~0.75Hz flat. (Does this mean guitars and pianos

Just don't use a guitar tuner. Or a piano. Your open C won't be C, it will be 440 * pow(sqrt(2,12),7) which is ~0.75Hz flat. (Does this mean guitars and pianos are out of tune? Yes.)