Coding and AI classes in Watford

An index number sets one chosen year to 100 and expresses every other year relative to it. The learner reads Watford Junction's yearly entries and exits from the regulator's table, picks the year to March 2020 as the base, divides every year by it and multiplies by 100. Python makes this a one-line list comprehension, and the resulting column reads like a recovery chart.

The index tells the true story at a glance: 82.3 means the station handled about 82 per cent of its pre-2020 traffic. Here is why percentages mislead. A fall of 80 per cent leaves a fifth of the traffic, and getting back from a fifth to the whole needs a rise of about 400 per cent, not 80. The actual rise from the low point, 313 per cent, is huge but still short. Add the two percentages, minus 80 plus 313, and you get a nonsense gain of 233 per cent; multiply the factors, 0.199 times 4.13, and you get the correct 0.823.

The same table shows that not every Watford station moved alike. Watford High Street reached an index of 105.0 in the year to March 2025, above its old level; Bushey reached 82.9 and Watford North 63.4. The regulator's single-year table adds a clue for Watford Junction: season tickets made up only about 8 per cent of its journeys that year. The learner writes a test that an index series always returns exactly 100 at its base year, and that chaining two percentage changes by multiplication gives the same answer as comparing the end points directly.

Checking a recovery claim against its base year is a strong reason for a Watford teenager to keep coding in 2026. The longer argument is in why teenagers should still learn to code in 2026.