At the time the RIAC START sheet was originally written (under the old Reliability Analysis Center), the RDC 2000 Handbook may only have been based on MIL-HDBK-217 (and its derivative) types of models, which were based solely on operating hour failure rates. With the advent of the old RAC PRISM methodology, since expanded by RIAC as 217Plus, reliability predictions could be performed based on operating, non-operating and power/temperature cycling failure rates, i.e., calendar hour failure rates. Care in predicting failure rates must be taken for two reasons: (1) the RIAC has licensed the 217Plus methodology to PTC (formerly Relex) and Isograph. Any other representation of the PRISM or 217Plus models would be in violation of copyright and may not have been implemented correctly. The PRISM and 217Plus models are not public domain. (2) You must be very careful if you try to combine operating-based failure rates and calendar-based failure rates. Operating-based failure rates do not consider nonoperating and cycling failure rates in their models, so there is no way that these failure rates from MIL-HDBK-217 or similar models can be converted to calendar hour failure rates. For 217Plus, the RIAC has published a Journal article on the correct way to convert a 217Plus calendar hour prediction to operating hours: