There are, however, some drawbacks to single factor metrics. Suppose the value for lines picked per hour this month was 67 and last month was 64. Has performance improved? The answer is "It depends." One must know something about the nature of the orders picked and hours worked, for example the sku spread, the proportions of "fast movers" and "slow movers" picked, and how well the total picking requirements matched the labor hours available in both months. In other words, to interpret a particular single factor metric, or to compare two values, one must have a considerable amount of additional information.