Coding classes in the Shetland Islands

A degree splits into 60 minutes and a minute into 60 seconds, exactly like hours on a clock. To convert 60.139 degrees, keep the whole 60, multiply the leftover 0.139 by 60 to get 8.34 minutes, keep the 8, and multiply the leftover 0.34 by 60 to get 20.4 seconds. So Lerwick's station sits at 60 degrees, 8 minutes, 20.4 seconds north, and its longitude of 1.183 degrees becomes 1 degree, 10 minutes, 58.8 seconds west. The learner codes those steps in Python in a few lines and they seem to work.

The bug appears when the seconds round up to 60. Rounding 59.964 seconds to one decimal gives 60.0, but by then the program has already fixed the minutes, so nothing carries over. Among a million evenly spaced values between 60 and 61 degrees, the step-by-step method prints an impossible 60.0 seconds 828 times, and 8,328 times if it rounds to whole seconds. The cure is to convert everything to seconds first, round once, and only then split into degrees, minutes and seconds with whole-number division. The learner also meets a quieter surprise: the computer stores 60.139 as 60.139000000000002899, so 0.139 times 60 comes out as 8.340000000000174, a reminder that decimals in binary are rarely exact.

Next, distance. Lines of latitude are evenly spaced, so a minute of latitude is always about 1.85 kilometres, roughly a nautical mile. Lines of longitude squeeze together towards the pole. On a spherical Earth, a degree of longitude is 111.2 kilometres at the equator but only 55.4 km at Lerwick, because the cosine of 60 degrees is one half. Finally the learner converts the file's own grid reference, 445300 east and 1139700 north, into latitude and longitude with the Ordnance Survey's published formulas, and lands about 94 metres from the stated 60.139, which is inside the rounding: a third decimal place of latitude spans about 111 metres.

Catching the bug that appears once in a thousand inputs is why a Shetland teenager should keep learning to code in 2026. The longer argument is in why teenagers should still learn to code in 2026.