A minor irrigation wing reports that the tanks in its own charge stood fuller at the close of the season than the tanks in the panchayats' charge — 62 in every hundred of capacity against 41 — and concludes that its own tanks are the better maintained. The wing's tanks were gauged from the depth read at the sluice; the panchayats' tanks from the mark the village watchman enters on the bund post. Which of the following is an assumption on which the wing's conclusion depends?

The wing's whole case is that 62 stands above 41, and that means something only if the two numbers were arrived at by tests that agree. A sluice depth and a watchman's mark on a post need not agree at all; if the post reading runs low by twenty points on any tank, the same water in the same tank yields 62 under one hand and 41 under the other, and the wing's conclusion is an artefact of its instruments. The assumption is therefore that the two agree. How many tanks each side holds bears on the size of the two groups and not on the gauging. Who pays the watchmen bears on his diligence, which is a separate charge the wing does not make. And whether every tank in the district falls under one of the two would matter only to a claim about the district, which the wing does not advance.