Field notes

Short pieces from the atlas desk. They are arguments, not a newsletter digest.

12 March 2026

Session windows that lie

A borrowed 30-minute timeout can invent engagement on one app and hide it on another. Write the physics before you plot the line.

2 February 2026

D7 during a paywall experiment is a treatment effect. Date it, or leave it out of the trend.

18 January 2026

Habit products and binge products do not share an honest weekly mean. Split the week or stop calling it a baseline.

9 December 2025

Coverage footnotes, legal constraints, and peer sets of one. Silence is sometimes the rigorous output.

21 November 2025

SDK sampling, logged-out users, and tablets. The missing people are often the ones your trend is about.