To improve verification of the Threshold Test Ban Treaty, the United States and Russia have embarked on an effort to make on-site yield measurements of each other's nuclear tests. Beyond their direct use in verification, these measurements also may prove useful in calibrating a monitoring system based on seismic magnitudes. The relative merits of seismic monitoring vis-a-vis on-site measurement have been at the core of a long-standing controversy. Many seismic verification problems hinge on statistical issues, including linear calibration based on a small data set and the formal use of expert opinion.