Making the invisible, visible.
The wondrous magical weather wand casts an enchanting spell of light. A way of making visible something that is normally felt. In less magical terms, I have an Arduino pro mini with a temperature sensor (currently a TMP36) and a RGB LED. The Arduino checks temperatures and sets the color of the light based on the temperature.
The early version of this used a temp to color table (like the temperature map project) that would for example set to the light yellow if above 70º or to blue if below 30º. However it would be pretty unlikely to encounter that wide of a temperature range within a space so instead of re-tuning the table for every location I wanted to have it set its own range.
The solution was to use statistics! It takes and averages the temperatures it sees and sets the color to normal (green) based on that average. The standard deviation (ie max/min range) is set based on the variation the sensor picks up. The color changes based not on a specific temp value but the number of standard deviations from that average. ie: 2+ stddev is red -2 stddev is purple, etc.
That worked for me because I wanted a way to paint with light and see temperature variation and I didn't really care about the specific temperature values.
More construction detail is available at hackster.io