An electricity division fitted a larger transformer at Kadipur in August and reports that voltage readings taken through September stood within the permitted band on every day, from which it concludes that the low voltage the village complained of has been ended. An answer to which of the following questions would be of most use in judging that conclusion?

September is the month after the rains, when the irrigation pumps are idle and the transformer is carrying its lightest load of the year, so a month of good readings may say nothing at all about the transformer and everything about the season. The two figures asked for close both gaps at once: earlier Septembers show whether the old transformer also behaved well in that month, and May and June show whether the new one holds up when the load arrives. The cost bears on value for money; the number of households and the maker of the transformer describe the installation, and none of the three tells us whether the good month was the transformer's doing or the calendar's.