Let us note, that, as it should do the formula _v'/v_ = E'/E shows that the unity is eliminated when the point in question is the estimate of relative values. It is needless to say that we do not insist on the practical possibility of the determination of the coefficients E and E', which intervene in the preceding formula. We have in effect said that the factors _d_, _h_ and _o_, do not appear to us determinable; we limit ourselves simply to showing here, the theoretical possibility of the system. What is important to remark is that in proceeding, as we have just pointed out, in all estimates of value and in consequence in the registration of all transactions, the variation in the value of the material support, corn, metal, etc. of the unity adopted does not intervene in any way. It will be further seen and we would insist on this point, that the common denominator of the value of things takes in this system, by the fact of its invariability, the character of a common measure; that it can in consequence be taken as unity, and considered in an abstract way. In fact this unity served once in a certain place and at a given moment to fix the initial value of things. From that moment it separates itself from the material thing which served to define it, which has momentarily represented it, and which has served as a support in our mind to effect the operations necessary to the relative fixing of the value of things. These operations made, it is of little consequence if the value itself of the kilogram of wheat varies, as is the case with the value of every thing else. Its initial value was for ever fixed, it can be taken as absolutely permanent and immutable,--the fundamental condition which a unity of measure ought to satisfy. In like manner original values of all kinds are equally constant quantities and anyone from among them might be taken as unity. In due course the actual values of things alter; varying continually, and it is the same with the kilogram of wheat or with any support whatever that has served to define the unity. The new values will always express themselves numerically by means of the fixed unity, although that has ceased to have a material representation. In practice the new numerical values will be obtained very easily; from the theoretical point of view they are fixed by means of the formula already given: _v'_ = _v_ × E'/E a formula which by the way, shows that if it happened that for anything at any moment and at any place, the elements _d_, _h_ and _o_ took values such that the term (_d'_ × _h'_)/_o'_ should return to a value equivalent to its initial value (_d_ × _h_)/_o_, the value of this same thing would again become identical with its initial value.