at the extremes, the actual percentage can range from 100 percent -- which means no learning occurs-to an unattainable Theoretical limit of 50 percent. At 50 percent, all units after the first require zero incremental time, because wherever total output doubles the average time is halved. For example, with a 50 percent learning curve and assuming the time required for the first unit is 100 minutes, then the average time per unit for a total of two units = 100 minutes * 50% = 50 minutes; an average of 50 minutes for two units equals a cumulative total time of 100 minutes, which is the same as for one unit. Smhus the 50-percent rate is an upper limit of learning and can never be reached.