I got out my Korg electronic chromatic tuner that I bought for tuning my guitars. They didn’t have these around 20 years ago when I used to play an alto saxophone.
I proceeded to play a G on the tenor sax. Not matter whether I jammed the mouthpiece right on, or had it tettering on the end of the neck, I could not get anywhere even close to a G tuned. I began to think that I was going to be forever destined to play by myself because I would not be able to tune to other instruments — I was around two semitones out!
Then it dawned on me! Doh!! Tenor saxophones are tuned to Bb; the Korg tunes to concert C — two semi-tones apart! Once I figured that a G played on the saxophone would register as an F on the tuner, I found that with the mouthpiece halfway on the neck cork, the saxophone was perfectly in tune!