New York Times: Sun Alert Lite has three dials with icons on them, one dial for skin type, one for the S.P.F. of your sunscreen, and one for weather conditions. The skin type dial provides adequate explanation of pigmentation, such as "Light brown skin, no freckles, good tanning ability,” to accurately pick your type. S.P.F. is self-explanatory, but the environment dial may require some thought.
For instance, at my downtown pool, where the chairs are on a grass lawn, do I choose "sunny urban” or "park open field?” When the dials are set, the app tells you how much time you can stay outside. Start the timer and it will count down to a warning beep with the message "time over!”