The HFT is calculated based on the architecture of a system. For example: an architecture with two valves with exactly the same function (1oo2) has an HFT of 1; when one of the valves fails, the other takes over the function. Although Hardware Fault Tolerance (HFT) resembles redundancy, it is not exactly the same. Consider, for example, a 2oo4 architecture with four transmitters (T1, T2, T3, and T4). At least two transmitters are expected to function. In this case, the HFT is 2, while the redundancy is 3.