Deviation (drilling terminology) is the angle at which the advancing direction of a borehole changes from one point in the borehole to another. This angle not only reflects the change of angle of inclination, but also reflects the change of azimuth, which is usually called the full angle change rate or borehole curvature.

Infinite Monkey Theorem: Let a monkey press keys randomly on a typewriter, and when the pressing time reaches infinity, it will almost certainly be able to type any given text, such as the complete works of Shakespeare.

Here, it is almost certainly a mathematical term with a specific meaning, and "monkey" is not a real monkey. It is compared to an abstract device that can generate infinite random letter sequences. This theory shows that it is wrong to regard a large but finite number as an infinite inference.

Ham sandwich theorem: given any ham sandwich, there is always a knife to cut it, so that ham, cheese and bread are just divided into two equal parts.

The ham sandwich theorem can be extended to the N-dimensional case: 1 If there are n objects in the N-dimensional space, there is always an n- 1 dimensional hyperplane, which can divide each object into two equal "volumes". These objects can be any shape, disconnected (such as slices of bread), or even some grotesque point sets, as long as the point sets are measurable.