BCal help system: The Tutorial
At the fishpond in question, there is in fact little doubt that the two layers are abutting. We are using an abutting relationship to represent a short-lived construction period before aquaculture commenced and so we would be happy to exclude the possibility of a hiatus on the basis of the archaeological evidence even though the radiocarbon evidence suggests that it is possible. Such decisions are often not this clear cut, however, and experts often do not agree exactly how archaeological evidence should be interpreted. This is not problematic when using BCal, it simply means that several models will need to be investigated and reported upon so that all possibilities are given an airing when the site reaches publication stage. Be open minded, consider all the archaeological possibilities and be sure to report on your findings so that others can share them too.
Since BCal uses a simulation approach (MCMC) to obtain the results it gives you there is one other important issue that you must consider (in addition to sensitivity analysis) before you assume that your results are reliable enough to report to others. This issue is convergence checking and we will focus on this now by considering the reproducibility of the results obtained for our fishpond example.