 For theoretical functions and relations, a particular problem arises from the idea that a theoretical term is, by definition, semantically dependent upon a scientific theory. Let us recall the above explanation of T-theoreticity: a term t is T-theoretical if and only if any method of determining the extension of t, or some part of that extension, rests upon some axiom of T. Let \(\phi\) be such an axiom and m be a corresponding method of determination. The present explanation of T-theoreticity, then, means that m is valid only on condition of \(\phi\) being true. The latter dependency holds because \(\phi\) is used either explicitly in calculations to determine t or in the calibration of measurement devices. Such devices, then, perform the calculation implicitly. A case in point is measurement of temperature by a gas thermometer. Such a device rests upon the law that changes of temperature result in proportional changes in the volume of gases.