In the context of quantum theory, recently we distinguished mathematics for expressing evidence from mathematics for
explaining evidence. Here this distinction is made in spacetime physics. We offer a system of mathematical thought-or as
termed in geodesy a reference system-for evidence, separated out from additional assumptions of a geometry in terms of
which to explain that evidence. The offered reference system for evidence, free of any assumption of a particular explanatory
geometry, whether Euclidean or general relativistic, amounts to a (theoretical) "assemblage of histories accumulated
in the memories of parties to a synchronous communications network."
The assemblage of histories gives voice to the known experimental finding, sometimes forgotten by theorists, that
any memory device for recording logical symbols must be insensitive to variations in signals in which those symbols are
carried. Out of acknowledging this insensitivity comes an appreciation of rhythms essential to the communication of digital
symbols and of the need for analog measurements to maintain these rhythms.
The separate reference system for evidence reconciles what otherwise is a conflict between the demand in quantum
mechanics for repeatable experiments and the lack in spacetime metrics appropriate to the Global Positioning System of
any exact symmetry, a lack that rules out an isometry between two spacetime regions for two occurrences of an experiment.