From here the paper stops asking one thing at a time. A two-step problem hands the answer of line one to line two as a given — so write each answer down, with its units, before moving on. One slip early rolls downhill.

And a new opening move: estimate before you compute. One order-of-magnitude guess — ten metres? a hundred? — costs five seconds and catches almost every socket slip, sign trap and bridge crossed backwards. The labels are off the drawings now, too: reading which number is which quantity is part of the exam.