Do accidentals last for the entire measure?

Today's musicians tend to react to the above question with raised eyebrows. Isn't it clear – accidentals in the key signature are always in force and for all octave registers unless annulled by natural signs. An accidental found in a measure is valid for this note and for the entire measure – no longer, no shorter.

1. Are accidentals effective for the entire measure?
2. How long is an accidental in effect for?
3. Does an accidental apply to the whole bar?
4. Do accidentals stack?

Are accidentals effective for the entire measure?

Accidentals usually apply to all repetitions within the measure in which they appear, unless canceled by another accidental sign, or tied into the following measure.

How long is an accidental in effect for?

Unlike the key signature, an accidental is placed within a measure, just before the altered note. Its effect stops at the end of the measure in which it is placed.

Does an accidental apply to the whole bar?

The accidental will apply to following notes in the same measure / bar but not after that. If it is needed to cancel the effect before then another accidental (maybe a natural sign) will be required. Oddly, although a sharp or flat in the key signature affects the same note in other octaves, an accidental does not.

Do accidentals stack?

The basic rule for stacking accidentals can be described as a zig-zag: start with the highest accidental in the chord and position it in the first column (immediately to the left of the chord), then the lowest in the second column, then the next highest in the third column, the next lowest in the fourth column, and so ...