Hello, I have a question in GRT. Suppose one is going to obtain the gravitational field of a point mass. He at first sets up a coordinate system. E.G., he may imagine laying out three rods throughout the space and put a clock somewhere. This clock may be put still at the origin of the rods frame or somewhere else. Now my question is, what is the difference? To put it in another way: suppose we use Swartzchild coordinate system, and then how do know by which clock the coordinate time is taken, just from the form of the metric?