 Next, we treat hypothetical calibration. For this, we need the notion of the limiting relative frequency of truths amongst propositions of a certain sort. The idea is that, for each proposition \(A\) in \(\mathcal{F}\), there is not just a fact of the matter about what the frequency of truths amongst propositions like \(A\) actually is; there is also a fact of the matter about what the frequency of truths amongst propositions like \(A\) would be if there were more propositions like \(A\). For instance, there is not just a fact of the matter about how many actual tosses of a given coin will land heads; there is also a fact of the matter about the frequency of heads amongst hypothetical further tosses of the same coin. In general, suppose we have a possible world \(w\), an extension \(\mathcal{F}'\) of \(\mathcal{F}\) (containing new propositions like \(A\)), and an extension \(\sim'\) of \(\sim\) to cover the new propositions in \(\mathcal{F}'\). Then there is a single unique number \(\mathrm{Freq}(\mathcal{F}', A, \sim', w)\) that gives what the relative frequency of truths amongst propositions like \(A\) would be were there all the propositions in \(\mathcal{F}'\) and where the relation of similarity amongst them is given by \(\sim'\), where this counterfactual is evaluated at the world \(w\). Again, let us illustrate this using our example of the coin toss from above.