Mental Maths Drill

Conventions: 1 n.mile taken as 2,000 yards, 1 knot (kn) as 100 yards per three minutes, the radian rule as 33 yards per degree per mile (35.25 exact, BR45 Vol 1 para 0221; 33 for bridge work, BR45 Vol 6 para 0416), and seconds per cable as 360 ÷ speed (30 s at 12 kn, 36 s at 10 kn), with the bridge approximations (27 − speed) × 2 for 11 to 16 kn and 38 − speed for 17 to 22 kn both scoring inside tolerance. Answers are marked to those conventions with tolerance, so a properly done mental answer scores even where the exact figure differs. Distance answers can be given in n.miles, cables or yards: set the unit beside the box and the marking converts, so the conversion is never the thing that fails you. Category toggles, unit choice and best scores save in your browser.