From a Number to a Decision
A sensor gives a number. A chart shows it. But what do we do next? Today you will learn how one line on a chart helps us make a decision.
For parents: a one-page guide — dinner questions and a family plan without a screen.
01Remember
This is the last lesson in “Measuring My World”. Think first, then open the answer.
What is the path from a sensor to an action?
Sensor → number → understanding → action. The sensor measures, we read the number, we understand what it means, and only then do we do something.
Why are numbers clearer on a chart?
At a glance you can see where they rise, where they fall and which one is the highest.
How do we know whether a number was measured or invented?
A measured number has a source — who measured it, when and with what. An invented number says that it is invented. In this lesson, too, the numbers are invented examples.
02Story
Many homes have a thermostat. You give it a number, for example 21 °C. When it gets colder than that line, the heating switches on. The line is like an invisible border: on one side we do nothing, on the other we act. This border is called a threshold.
There are thresholds in the big world, too. The National Institute of Meteorology and Hydrology in Bulgaria issues warnings in three colours — yellow, orange and red — for the next 48 hours. Its map is updated every day.
Specialists in indoor air use about 1000 ppm of carbon dioxide as a signal to open a window. You met it in the lesson about air.
Experts set those thresholds. Your threshold in this lesson is a learning one: you make it with your family or class to learn how a number becomes a decision. It is not an official standard.
03Worked example
In an invented room the temperature climbs during the day and reaches 27 °C. The family decides: “When it reaches 26 °C or more, we close the blinds and drink water.” Here is how they get there:
Number
During the day the thermometer shows 21, 22, 23… up to 27 degrees.
Chart
We plot the numbers as dots and join them with a line. We see the room warming up.
Threshold
We draw a horizontal line at 26 °C. Dots on or above it mean: “Time to act.”
Decision
We write it in words: “When it reaches 26 °C or more, we close the blinds and drink water. Then we check again.”
04Try it
1 · Predict
If we put the threshold very low, near the smallest number, how often will we have to act?
2 · Run: move the threshold
Pick an invented series of numbers. Then drag the orange line up and down — with a mouse, a finger or the arrow keys. The slider below works too.
3 · Change: build “our threshold for action”
The threshold is the one from the chart above. Choose what you do, who does it and when you check again. Nothing is typed and nothing is remembered.
05No screen: “Our threshold”
You need: a sheet of paper, a pencil, a ruler and your family (or class). About 20 minutes, no screen.
Choose one thing you notice at home or in class: is the room warm, is it noisy, is the air stuffy? If you have a thermometer, use it. If not, rate it by feeling from 1 (very good) to 5 (very bad).
Write the numbers for one day, a few hours apart, in a table: when · how much.
Draw a chart on the paper: hours along the bottom, numbers up the side. Join the dots.
Draw a line where everyone thinks we should start to act. Argue about it — that is the most important part! Why here and not higher up?
Write a sentence: “When … reaches … or more, we … Then we check after …” Stick the paper somewhere you can see it.
After a week, talk about it: did it help? Did we act too often or too late? Move the line if you need to.
Keep the actions simple: open a window, drink water, close the blinds, talk more quietly, ask an adult. Do not touch sockets or appliances you do not know.
06Make your own
Make an “Our threshold for action” card for your family or class.
- At the top write what you measure and how (a thermometer, a sensor or a feeling from 1 to 5).
- Draw a small chart with the threshold line.
- Write the sentence and who is responsible.
- Add a review rule: “We look at the line again after … and move it if …”.
- Show the card to a teacher or parent. Ask: “Is our threshold reasonable?”
- Explain it to someone: with the card in your hand, explain to a younger brother, sister or classmate what a threshold is and when we act.
- Make it for someone: make a “Time to air the room!” sign for your class or for your grandma's room: which number is the threshold and what we do then. Put it up somewhere visible only with your teacher's or parent's permission.
07What I learned
- A threshold is a line on a chart: when a number reaches it, we decide to act.
- A threshold set low means acting almost all the time. Set high, it means acting late. There is no single “right” threshold — it must be reasonable and talked over.
- “Our threshold for action” is a learning agreement of a family or class. Official thresholds are set by experts.
A thermometer and a chart tell you when a room has overheated. And how do you know when you need a rest?
Check yourself
1. The threshold on a chart is…
2. The threshold is set very low. What happens?
3. “Our threshold for action” in this lesson is…
It is yours when you can put a threshold on a chart, explain why it is there, and write a plan with “when… then…”. No points and no rankings — just a skill.
08I have a question
Do you still have a question? Write it here. It goes to your parent, not to strangers. Your parent confirms their e-mail first.
The form is loading… If it does not appear, write your question on paper and show it to a parent or teacher.
·Sources
- Title: From a Number to a Decision (DB-IS-12) · Author: Children's Library, East Accelerator Foundation · Source: original content, 2026; the numbers in the examples are invented · Rights: CC BY-SA 4.0.
- NIMH warnings in three colours (yellow, orange, red) for the next 48 hours: BTA — “НИМХ — кодове за опасни явления” (NIMH hazard codes; in Bulgarian), seen 01.10.2026 (the page has no date). Current warnings — only from the NIMH website.
- The guide value of about 1000 ppm CO₂ for ventilation: working group of the German Federal Environment Agency, “Gesundheitliche Bewertung von Kohlendioxid in der Innenraumluft”, Bundesgesundheitsblatt 51 (2008), abstract (in German and English), seen 01.10.2026.
- Licence: CC BY-SA 4.0 · Children's Library, East Accelerator Foundation, 2026. You may share and adapt this lesson if you credit the author and keep the same licence. Learning is free forever.