[Richard777 (OP)]

The Lorentz factor defines a change to the properties of an object in motion. It may be called a “change factor”. It is also useful to define an “incremental change factor” (a first differential).

A gravitational field may be represented as a field vector. The field may change, and the vector magnitude changes also. The change in magnitude may include a “change factor” such as the Lorentz factor.

Assume a field changes twice, and two change factors are required (one for each change). The change factors may be;

   - the Lorentz factor
   - the incremental factor

Combination of the change factors will give a complete transform and lead to the Schwarzschild metric.
(see attachment)