Visual explainers

Five small pages you can poke at. Each one goes with a lesson, uses that lesson's fictional company and data, and checks its own math against the lesson when it opens. They work offline: open a file by double-clicking it.

• Join fan-out explorer

  Give a customer a second address and watch the joined row count and SUM grow, then fix it four ways. Ends with a planted fan-out to find.

  Lesson 01-02 Joins without losing rows (Brightcart)

• Window function playground

  Pick PARTITION BY, ORDER BY, the frame and the function, and see which rows each value is worked out from. Shows the RANK vs ROW_NUMBER tie and the default RANGE frame trap.

  Lesson 01-03 Window functions (Fernhill Supply)

• Cohort triangle builder

  Build the retention triangle from raw events, then switch unobserved months from blank to 0 and watch the averages fall. Ends with a planted mistake to click.

  Lesson 01-04 Cohort retention (Tallyo)

• A/B test calculator

  Sliders for visitors and conversions, a live z-test, p-value, confidence interval on the lift and sample ratio check, plus a seeded peeking simulation that reproduces lesson 02-13.

  Lessons 02-03 A/B test from scratch and 02-13 A/B test pitfalls (Tidewater Outdoor)

• Agent loop stepper

  Step through recorded agent runs one model call at a time: the reply, the guard, the observation, the growing cost and the number grounding check. Then flag the ungrounded number yourself.

  Lesson 06-13 An analytics agent loop from scratch (Larkspur Goods, simulated fixture)