Leveraging powerful -- yet simple methods of reliability data analysis of repairable products or systems can help you stay on the right track. Typically, data on repairable products are obtained through field, repair or warranty information. Repairable products -- unlike nonrepairable ones -- can lead to multiple event times on the same unit, or recurring events, resulting in recurrence data. Recurrence data require special methods of analysis. Many questions about the reliability of a repairable product, based upon field repair recurrence data, can be answered by estimating its mean cumulative function (MCF). The MCF of a product at age t is defined as the average number of failures per unit up to time t. In estimating the MCF, the exposure time could vary appreciably from unit to unit within orders. This may be because of staggered entry of units into the field or differences in use rates.