Camille's answer below is excellent. The only comment I have is don't set a "time" on when you will re-check if the piano needs tuning. Camille's tips on how to know when a piano might benefit from a tuning are a better gauge than time. My piano gets bright, zingy, and plinky and it aggravates me so much I get it tuned then. If I could afford it, I'd get my piano tuned four times a year, once for each season, just because the sound changes and it bugs me. I do have a humidifier for it, which helps.

"In C" may work, but it could leave confusion as well, if someone was asking for the key one is playing in rather than what key the instrument is in. Plus, some (mainly folk/ethnic) instruments are limited to diatonic scales and can only play in one key, with several versions of the instrument for different (concert) keys. Referring to concert pitch is more accurate in the long run.

This is a V/V progression. The octaves tell everything that is going on. C-F-Bb-Eb-Ab. The lower bass notes are moving in 5ths as well.

Just by changing "tools" to "techniques" makes this a suitable question.

@Tim, perhaps. But many singers also do not have the privilege of always practicing with accompaniment. I still think it harder for singers than instrumentalists, but that may just be a matter of opinion.

In vocal music keeping both keys in flats would make for an easier transition for the singer who has to "find" pitches. I have seen some piano pieces where the modulation included a transition from flats to an enharmonic sharp key, but that is easier to do when you get the pitch you need just by hitting the right key. It's much harder to make the adjustment from flat to sharp and vice-verse while singing.

Also, saxophones are extremely sensitive to being bumped. It could be that a key is no longer covering a hole exactly right.

@Pyromonk, no one can tell you whether or not your set-up works for you. Each person is unique and will respond differently to different reeds, mouthpiece bores and apertures, etc. One reason there are so many to choose from! You can't decide from looking at a picture or knowing a name. These things must be tried out. If you have any questions, make an appointment with a good shop and try out some things. Do you have a teacher? Someone watching you play may know if there is something that changes in your physical playing to cause notes to go out of tune.

@Sam, you are right about the shortcomings of uprights pianos, in addition to their poorer sound quality. They have a good purpose but they can fall short of the needs of very advanced pianists.

@PiedPiper, no I thought you were talking about the 8th note F#. Agree about the half-note if it was written for two players instead of piano. But, still nothing in Gould's book about two parts on the exact same pitch at the same time, a note with two stems. I assume that is just one accidental. I looked at pg.79.

Yes, the accidental pertains to the staff, not the part. More specifically, it pertains to the line/space. The first-space F is sharped in this measure, but no other F. If another note was shown on the fifth-line F, it would need an additional sharp sign if it was to be sharped.