Labor-Days

The term "man-days" is the more traditional term here, but that term uses the male noun in reference to human beings in general, a usage which has come to be prejudicial to some people. The term "labor-days" has been used in Marxism, and could bring some Marxist baggage with it, but this seems less of a problem than the problem with "man-days." In any case, the point is that labor must be measured in units of labor-time per unit of time in production -- that time enters twice, since labor is a service. To be quite right, we would measure the input of machinery (of a specific type) by machine-days per week, to put machine services on the same basis as labor services for cost comparisons.

It is, of course, difficult to avoid gender bias while writing in English, or (I suppose) most other natural languages. "His or hers" can often be cumbersome, though I have used it somewhat. I have also used examples with "his" and "hers," and have attempted to do this more or less at random. Exercise: do a statistical analysis to find out whether I have succeeded. Let me know the result.