Peters' length (Pe'-ters). A horizontal distance between the points on the side of the potential-field (usually, magnetic) anomaly profile, where the slope line is drawn at half of the maximum slope line. This measurement is made with the objective of determining the depth of an anomalous mass (magnetized body). For tabular body or dike models, the Peters' rule gives a depth as 5/8 of the Peters' length (Peters, 1949).