← ACARA Digital Technologies Years 9–10

Recording sensor readings in a spreadsheet with timestamps

A sensor log stores each reading as its own row: a timestamp column for the date and time, then one column per measurement, with units in the header, such as Temp (C).

Part of: ACARA Digital Technologies Years 9–10 — Acquiring and Validating Data — Module 36

Understanding Recording sensor readings in a spreadsheet with timestamps in ACARA Digital Technologies Years 9–10

What it does: Three readings taken 15 minutes apart sit on three separate rows, each starting with its own timestamp. The unit (C) is in the header, so the cell holds just 22.4 and can be used in formulas such as AVERAGE. Typing 22.4C in the cell would turn it into text. A sensor log uses one row per reading, so each new measurement goes in a new row and the table grows downwards. Each measurement gets its own column, so temperature and humidity are kept separate and can be analysed separately. One reading per row: a timestamp followed by its measurements. The wrong answer squeezes two readings into one row.

Common mistakes: This reading row is missing its humidity value, so it has fewer columns than the header. Each row needs a value for every column: 2025-03-01 09:00,21.5,48. The unit is written inside the data cell, which turns the number into text. Units belong in the header, Light (lux), so the cell holds only 310.

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This module's key terms are also in a printable crossword (Modules 255–329) and word search (Modules 226–329).

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Learning
Duo
How should a sensor log store each new reading?
Added onto the end of the previous rowAs its own new row
Matches
Temp,Humidity,Light 22.4,58,640
↓
There is no timestamp column, so you cannot tell when each reading was taken, and the headers have no units.
Applying
Meanings
Term
one row per reading
Meaning
A sensor log stores each reading as its own row: a timestamp column for the date and time, then one column per measurement, with units in the header, such as Temp (C).
Practice
Timestamp,Temp (C),Humidity (%)
Testing
Gaps
Timestamp,Temp (),Humidity (%)
Check Answer
Spots
1Time,Temp (C),Humidity (%)
22025-03-01 09:00,21.5

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Quick Questions

1. How should a sensor log store each new reading?
A. Added onto the end of the previous row
B. As its own new row ✓
A sensor log uses one row per reading, so each new measurement goes in a new row and the table grows downwards.
2. Which column should come first in a sensor log?
A. The average of all readings
B. Timestamp (date and time) ✓
The timestamp column records when each reading was taken, so it usually comes first. Averages are worked out later.
3. Which header is better for a temperature column?
A. Temp (C) ✓
B. Temp
Putting the unit in the header, like Temp (C), means anyone reading the log knows what the numbers measure. The cells can then hold just the number.
4. A logger records temperature and humidity every minute. How many measurement columns does the log need?
A. Two: one for temperature and one for humidity ✓
B. One shared column for both measurements
Each measurement gets its own column, so temperature and humidity are kept separate and can be analysed separately.
5. Which is the better way to record a reading in the Temp (C) column?
A. 21.5 ✓
B. 21.5 degrees Celsius
The unit belongs in the header. Keeping only the number in the cell lets the spreadsheet treat it as a number for formulas like AVERAGE.

Match the Pairs

Timestamp,Temp (C),Humidity (%) → A header row: a timestamp column first, then one column per measurement, with units in brackets
2026-03-02 09:15,22.4,58 → One reading stored as a single row: the date and time, then the temperature and humidity measured at that moment
Each new sensor reading is added as its own row, so the log grows downwards → 2026-03-02 09:15,22.4 2026-03-02 09:30,22.9 2026-03-02 09:45,23.1
Putting the unit in the header means each cell holds only a number, which can be used in calculations → Temp (C) | 22.4
Temp,Humidity,Light 22.4,58,640 → There is no timestamp column, so you cannot tell when each reading was taken, and the headers have no units.
Timestamp,Temp (C) 2026-03-02 09:15,22.4,58 → The row has three values but the header has only two columns, so a measurement has no column or label.

Key Term

one row per reading
A sensor log stores each reading as its own row: a timestamp column for the date and time, then one column per measurement, with units in the header, such as Temp (C).

Fill in the Blanks

1. Timestamp,Temp (C),Humidity (%)
Hint: Type the unit symbol for temperature in degrees Celsius, shown in brackets in the header.
2. Timestamp,Temp (C),Light (lux)
Hint: Type the header of the column that holds the date and time of each reading.
3. =MAX(A2:A50)
Hint: Type the function that finds the largest value, which gives the latest timestamp in the log.
4. =COUNTA(A2:A50)
Hint: Type the function that counts non-empty cells, so it counts the readings because each reading has its own row.
5. Timestamp,Temp (C),Humidity (%)
Hint: Type the unit symbol for relative humidity, shown in the column header.

Spot the Error

Question 1
A Time,Temp (C),Humidity (%)
B 2025-03-01 09:00,21.5
C 2025-03-01 09:10,21.8,47
D 2025-03-01 09:20,22.1,46
Line B — This reading row is missing its humidity value, so it has fewer columns than the header. Each row needs a value for every column: 2025-03-01 09:00,21.5,48.
Question 2
A Time,Light (lux)
B 2025-03-02 08:00,310 lux
C 2025-03-02 08:05,325
Line B — The unit is written inside the data cell, which turns the number into text. Units belong in the header, Light (lux), so the cell holds only 310.
Question 3
A Time,Temp (C)
B 10:00,18.2
C 09:05,18.4
D 10:10,18.7
Line C — The timestamp is out of order. Readings are logged in time order, so after 10:00 the next row should be 10:05, not 09:05.
Question 4
A Time,Temp (C),Moisture (%)
B 2025-04-01 07:00,15.2,40
C 2025-04-01 07:30,15.9,39
D 2025-04-01 08:00,16.4,high
Line D — The Moisture (%) column should hold numbers only. The word 'high' is text and can't be averaged or charted. It should be the number 38.
Question 5
A Time,Temp,Humidity
B 2025-03-01 09:00,21.5,48
C 2025-03-01 09:10,21.8,47
Line A — The header is missing the units. Each measurement column should show its unit, e.g. Temp (C) and Humidity (%), so the numbers have a clear meaning.

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