What is the "cross" type in the autofocus points of 5D3 and 7D mentioned in the Canon camera manual? What do the 61 o'clock and 19 o'clock of the two planes mean?

There are straight-line, cross-shaped and double-cross-shaped automatic foci, and the focusing accuracy is also from low to high, and the double-cross in the center has the highest focusing accuracy. . . 61 or 19 o'clock indicates that there are 61 or 19 focus points in the whole framing range. As long as one focus point is in focus (the square of the focus point turns red), the camera will give a prompt tone, and the focus indicator light will light up, and the shutter can release the photo. Novices can automatically select the focus point, and after they are skilled, they can manually select the focus point according to their own needs. In the end, they often use single-point focus, that is, they only use the double cross in the center with the highest accuracy to focus. . .