A jaggery unit fitted a furnace of a new pattern and found that over the fortnight after it was fitted the unit burnt 18 in every hundred less bagasse for each quintal of jaggery made. The owner concludes that the new furnace has cut the unit's fuel. Which of the following, if true, most strengthens the owner's conclusion?

A fortnight is a short window on a quantity that used to swing by a quarter from fortnight to fortnight, so the 18 could easily be one of the unit's ordinary swings and nothing to do with the furnace. Holding the saving across a whole season, over every grade of cane and in both kinds of weather, takes it well outside that ordinary swing and removes the alternative explanations at the same time. The builder's experience elsewhere is a reason to expect a good furnace, not evidence about this one's effect. Who kept the figures speaks to their honesty, which is not in doubt. And a costlier bagasse makes the saving more welcome without making it more real.