The Time Between Failure (TBF) formula is a key metric used to measure the reliability of a system. It is a measure of the average time that passes between system failures. This metric is important for assessing the reliability of a system, as it can help to identify areas of improvement and identify potential problems. The TBF formula is calculated by dividing the total operating time of a system by the number of failures that occur during that time. This gives an average time between failures, which can then be used to compare the reliability of different systems. TBF is an important metric for assessing the reliability of a system, as it provides a clear indication of how reliable a system is and can help to identify areas for improvement.