Four Little Weights Will Settle Any Order1 · 3 · 9 · 27 — and the beam does the rest
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To weigh outdrachm of saffron
Right — pull up a stool. That heap's already weighed onto the left pan at your order. Now drag my brass on. Too heavy on the far side? Then that weight belongs IN with the saffron, not against it — drop it on the goods' own pan and it takes its own weight straight off.
the felt block
Left pan lightens what's there; the far pan piles it on. So every order from one to forty is just some of these four added and some taken away — 27 − 9 + 1 is nineteen, and off you go. Go on, have a shift at it.