I’m sitting at a warung in Central Sulawesi, waiting to pay for my coffee. Two coffees, in fact, and two cakes. The warung owner whips out a calculator and starts to punch numbers into it: 2000 + 2000 + 1000 + 1000 = 6000. I gave him a 10,000 rupiah note. ‘Clear’, he punches. Then 10,000 – 6000 = 4000, and he counts out two 2000 rupiah notes and gives me my change. Meanwhile, other clients wait for their coffee. Is it really possible that he can’t do these sums in his head?

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