Failure identifies the average number of hours until failure occurs. Lambda identifies the number of failures expected per hour. Reliability is the probability that a failure will not occur during a specific span of time. Failure rate relies on logarithmic math to simplify calculations using that is very similar to the type of analysis used for electronic circuits. Overall failure rate for a complex item is the sum of all the failure rates for all of the individual components in the item. This applies to situations where failure of one component causes the entire item to fail. The type of calculation is similar to a series electronic circuit. Overall failure rate for items with full redundant overlap is the inverse of the sum of MTBF for all of the individual redundant items. This applies to situations where all of the components in the item must all fail before the item fails. The type of calculation is similar to a parallel electronic circuit. A reliability block diagram is used to construct a model for large items. This provides traceability when funding and manpower requirements are identified using reliability calculations. Failure rate for silicon and carbon devices doubles for each C temperature rise. Electronic devices operating at C will fail 64 times more frequently than the same kind of items operating at C. This relationship holds true above C. Transportation reliability is similar, but values are expressed in terms of distance, such as fault per mile or faults per kilometer. Failure rate can be expressed in terms of the number of cycles. Thermal shock caused by heating and cooling can induce failure when power is cycled on and off. Most mechanical switches are built to operate 10,000 cycles before failure, which is about 30 years for a cycle rate of 1 action per day. Distance, cycle, and decay reliability all have separate contributions that effect the overall failure rate. Availability Availability is generally used with systems that incorporate periodic maintenance. Availability is the probability that an item will operate correctly during a period of time when used at random times during that period. Available time is the time while the system is fully operational. Down time is the time while the system is unavailable for normal use, and this consist of the time while periodic maintenance is being performed and the amount of time while the system is faulted. Availability calculations are