The efficiency of the mechanism is 30%. What does it mean?

The efficiency of a mechanism is the ratio of useful work to the work that the mechanism has expended. This means that when you calculate mechanical work using the formula A = F × S, it is considered useful. In fact, the device usually requires much more power to perform the same action. An efficiency of 30% means that only 0.3 part of the total energy will be used to perform an action (most often the rest is converted into heat). When you use work A in formulas, it should always be multiplied by the efficiency value.