Question

describe how chaining is done when the endpoints are not visible from the intermediate pooint

Answer 1

Though it is desirable to select stations so as to avoid obstacles, occasionally the obstacles are unavoidable.

Various obstacles to chaining may be grouped into:
(i) Obstacles to ranging (chaining free-vision obstructed)
(ii) Obstacles to chaining (chaining obstructed-vision free)
(iii) Obstacles to both ranging and chaining.

Various methods of overcoming these obstacles are explained is this article.
Obstacles to Ranging

These obstacles can be further classified into the following categories:
(a) Both ends of the line are visible from some intermediate points. Intervening ground is an example of such obstacle. By resorting to reciprocal ranging this difficulty can be overcome.
(b) Both ends of the line may not be visible from intermediate points on the line, but may be visible from a point slightly away from the line. Intervening trees and bushes are the examples of such obstacles.

Answer 2

The use of an intermediate end point in preventing diabetes is based on the general concept of the progress of early incidence of immunological and metabolic changes in manifest types of 1 diabetes.

In this way, these markers are suitable for trials pf two randomized phase, which can speed up the promise of new therapies and can be confirmed in phases gradually in three phases.