TelemetryData lesson
Did the classroom air change, or did the network retry?
A 15-minute data lesson for grades 9–12. The readings below are invented. Print this page or download the CSV. No hardware, account, or student data is needed.
The question
A sensor measures CO₂ every ten seconds. Its network sometimes sends the same reading again. Each row below is a delivery; reading_id identifies the measurement. Did the sensor take six measurements or four?
reading_id | Measured second | co2_ppm | Delivered second |
|---|---|---|---|
| r1 | 0 | 600 | 1 |
| r2 | 10 | 650 | 11 |
| r3 | 20 | 700 | 21 |
| r4 | 30 | 750 | 31 |
| r4 | 30 | 750 | 32 |
| r4 | 30 | 750 | 33 |
Try it in class
- Predict whether a network retry can change the average when every delivered row is counted.
- Circle rows whose reading_id has already appeared. Count deliveries and distinct measurements.
- Calculate the mean CO₂ value with every row, then with one row per measurement. Which mean answers the question about the four measurements?
- Name one thing you would need to check before using real readings to make a ventilation decision.
Teacher check
There are six deliveries and four measurements. r4 arrived three times. The all-row mean is 700 ppm; the distinct-measurement mean is 675 ppm. Neither is a time-weighted room average without a sampling assumption. Real interpretation also needs sensor accuracy, placement, and missing-reading checks. These invented values are not a health assessment.
What if the network retries again?
Keep the four measurements fixed. Change how many extra copies of the last reading arrive, then compare the averages.
- Delivered rows
- 6
- Average of delivered rows
- 700 ppm
- Average of four measurements
- 675 ppm
Only the delivery count changed. The sensor did not measure the room again.
Optional product extension
The exercise works offline. You can query these same invented rows in the browser SQL playground without an account. A separate first-event guide shows how to send synthetic events to Telemetry; its $0 plan includes 1 GB of storage and needs no credit card. Have a teacher review any cloud use before students participate.
Query these rows in the browser (no account)First-event guideFree-plan details
I built Telemetry. I prepared this activity with AI help, and it has not been classroom-tested. Please review it before teaching.
Teachers: found an error or adapted the exercise? Email me your notes, without student data.