Coherent breathing

Five and a half seconds in, five and a half out. About five and a half breaths a minute, held for as long as you like.

Sit however you are comfortable. You can close your eyes; the count is spoken on the screen, not out loud.

The pattern

in through the nose, out through the nose

The long sit. Even, symmetrical, nothing to count wrong. Good under headphones and good for twenty minutes.

What is known

Around six breaths a minute is where breathing and heart rate line up most strongly. The rate matters more than the exact numbers, so drift a little and it still works.