In many ways, academic disciplines are sources of knowledge in a similar way to the 'Paris one meter." When an academic discipline offers a piece of knowledge it doesn't necessarily mean that the piece of knowledge is objectively true. Instead, the discipline creates a procedure or method that produces a piece of knowledge that is true insofar as the procedure or method is acknowledged as the standard for that truth. The procedure or method may change over time, with new technologies for example, and therefore the piece of knowledge might also have to change. This is true for the following academic disciplines:

Anthropology

Psychology

History

All disciplines, though to varying degrees