c4.

Middle C is marked as "small c (c1)" in Helmholtz pitch notation.

But middle C is labeled "C4" in Scientific pitch notation.

c4. The middle c is a Western music term, which represents the note value located in the middle of the large staff, or is equivalent to "c4" in scientific pitch notation. Middle C is also in the middle position on keyboard instruments (such as pianos), and is usually the lowest C that can be produced by female voices or unaltered male voices.

Middle C is a pitch with a frequency of 261.63 Hz (in the past it was specified as 256Hz). It is the 49th of 97 tones in the musical sound system. Middle C is located in the center of the musical sound system. The sound group of middle C belongs to a group of small characters in the musical sound system, and has a fixed singing name of "do".

Correct hand shape:

1. Place your hand on the piano, arch your palm, separate your five fingers, let your fingers droop naturally, touch the keys with your fingertips, and form a semicircle with your entire hand.

2. The part where the second, third, fourth and fifth fingers touch the keys should be the fingertips, not the belly of the fingers; the thumb touches the keys on the outside of the fingertips.

3. The back of the hand should be balanced and should not be tilted toward the little finger; it should feel closer to the thumb.

4. When playing, keep the semicircular shape of your hands. Your fingers should not be stretched too straight or too bent. The first joint of your fingers must stand straight.

5. Trim nails regularly to ensure standard hand shape when playing.

Reference for the above content: Baidu Encyclopedia-Central C