To calculate the failure rate and MTBF of a resistor using the MIL-HDBK-217F failure model, thermistor or variable resistor, enter its parameters in the following table.
(1) Established reliability styles are failure rate graded (S, R, P, M) based on life testing defined in the applicable military device specification. This category applies only to three-letter styles with an "R" suffix, such as RCR or RLR. Also see the quality table.
(2) Resistor Case Temperature. Can be approximated as ambient component temperature for low power dissipation non-power type resistors.
I have made this letter longer than usual, only because I have not had the time to make it shorter.