It is of no use rushing in with picturesque paradoxes, such as 'Space caught bending,' if you have not mastered this fundamental conception which underlies the whole theory.
When I say that it underlies the whole theory, I mean that in my opinion it ought to underlie it, though I may confess some doubts as to how far all expositions of the theory have really understood its implications and its premises.
Our measurements when they are expressed in terms of an ideal accuracy are measurements which express properties of the space-time manifold.
Now there are measurements of different sorts.

You can measure lengths, or angles, or areas, or volumes, or times.

There are also other sorts of measures such as measurements of intensity of illumination, but I will disregard these for the moment and will confine attention to those measurements which particularly interest us as being measurements of space or of time.

It is easy to see that four such measurements of the proper characters are necessary to determine the position of an event-particle in the space-time manifold in its relation to the rest of the manifold.

For example, in a rectangular field you start from one corner at a given time, you measure a definite distance along one side, you then strike out into the field at right angles, and then measure a definite distance parallel to the other pair of sides, you then rise vertically a definite height and take the time.