Описывается принцип измерения центрирования цилиндрических линз (этот пункт называется Centration measurement). Контекст:

Definition: Cylinder centration is the rotation angle of the cylinder bus. For a cylinder, when we rotate it as 180 degree along the C direction, we will find than the cylinder bus will not coincide. We call this as the centration of the cylinder.

И затем такой абзац:

For centration measure, we need an assistant body, put the cylinder lens close to the body as the Fig.A.12 shows. At this time the bus line is the black line in the fig. Then rotate the sample to 180 degree, and close to the body again, we will find that the bus line position is moved to the red line position. The angle between the black and red line is the centration of the cylinder sample. No matter the measring mode is transmission or reflection, they all base on this principle.

Это весь текст в данном пункте.

Спасибо за любую помощь!

предположительно и имхо:

cylinder bus = cylinder lens bus = ось цилиндрической линзы

Cylinder centration = Cylinder lens centration = центрирование цилиндрической линзы

Детальнее тут и там.