J. Bigelow and R. Pargetter are interested in quantity insofar as this provides scope for the application of their overall metaphysics. Bigelow and Pargetter address long-standing ontological questions about quantities. Extensive quantities like mass and length are directly measurable in that measurement scales for them can be set up without presupposing that anything else is measurable. The operationist holds that objects only form composites when suitably juxtaposed and only stand in numerical relations like 2M when actually measured. Comprises axioms which lay down the formal properties needed to guarantee certain results about the application of numbers to things, particularly with regard to scales of measurement. Concatenations of length are different from concatenations of mass, and these distinctions must be preserved for each extensive quantity. The Archimedean axiom is important because it guarantees that a so-called standard sequence is possible for a given scale for extensive measurement.