A weather utility that ships with Fahrenheit as the default will hear about it on the first afternoon in Malaysia. That is not the interesting part. The interesting part is what people do when they open Units and find a list that also contains wind in knots, pressure in inches, and visibility in miles.
We sat with eight people in Petaling Jaya who had never used the build under study. Each person already checked weather on the phone they brought. The task was: make this app show the temperature the way you usually read it, then make the rain amounts match what the evening news uses.
Seven of eight found temperature quickly. Rain was slower. Millimetres sat next to inches under a heading called Precipitation, a word two testers said they would not look for. They looked for Rain. One person changed wind units by accident while scrolling and did not notice until the debrief.
The control that “kept” Celsius after a reinstall was not in Units. It was under Appearance, behind a toggle called Follow system. Testers who had already set Celsius in Units thought they were done. After we asked them to clear the app’s storage and open it again, six of eight were back on Fahrenheit.
Unit settings are not a preference page people visit for pleasure. They visit it when something looks wrong. The labels should be the words they will use in that moment — temperature, rain, wind — and the choice should survive a reinstall unless the person asks otherwise.