Joe Brook Smith was the first to propose use of an exact scale track gauge in July 1964, when also the term Protofour was invented by Malcolm Cross.
Just as in the prototype railway, on a model the wheel-rail interface is the fundamental aspect of reliable operation.
So as well as a track gauge, P4 also specifies the wheel profile and track parameters to use, which are largely a scaled-down version of real-life standards with some allowances for practical manufacturing tolerances.
P4 standards are promoted worldwide by the Scalefour Society, which is based in the United Kingdom.
The standards document is hosted by the Scalefour Society[3] and the society's Central London Area Group (CLAG) make a HTML version available.