ACARA v9 CONTENT DESCRIPTION “use equipment to observe, measure and record data with reasonable precision, using digital tools as appropriate”
Builds on earlier measuring with rulers and thermometers. Now the focus is precision: choosing the right unit, reading the finest mark on a tape or the digits on a digital sensor, getting level with the scale, and repeating each reading so the recorded value can be trusted and compared.
What reasonable precision means
Precision is how finely you read and record a measurement. A tape measure has millimetre marks, so a shadow that ends between 14 and 15 centimetres is read to the nearest millimetre, such as 14.3 cm, not rounded carelessly to a whole number. Reasonable precision means matching the reading to what the instrument can show: the right unit, the finest mark you can read, and your eye level with the scale, straight on. Reading from an angle or rounding too soon throws away detail the tool was built to give.
Read the tape: log shadow lengths to the nearest millimetre
A stick's shadow was measured with a tape each hour through the afternoon and the lengths were read to the nearest millimetre. Switch between the table and the chart to see the same careful readings two ways.
The table holds the exact shadow length you read off the tape each hour, to the nearest millimetre. The chart turns those same precise readings into a shape, and the steady climb shows the shadow stretching as the Sun sank lower.
Digital tools and logging data
A digital thermometer or sensor reads the value for you and shows it as digits, often to a tenth of a unit, finer than you could judge by eye. When it shows 21.4 degrees, that tenth-of-a-degree digit is part of its precision. A digital tool can also log each reading the moment it is taken, building a record with the unit attached. You still set it up carefully and read it the right way, but the tool removes the guesswork of reading a fine scale and keeps a clean, time-stamped record you can check later.
Record temperature: a digital sensor logs each reading
A digital thermometer logged the air temperature on the hour through a spring morning, to the nearest tenth of a degree. The bar chart and the line graph are two ways a digital tool can show its logged readings.
Each bar is one reading the digital thermometer logged on the hour. The sensor reads finer than your eye and records the value with its unit straight away, so the warming through the morning shows up as a steady, trustworthy climb.
Watching for a reading that does not fit
When you record readings that should change smoothly, one number sometimes jumps far from the rest. That odd value is worth a second look. Perhaps the tape slipped, the sensor was knocked, or you read the wrong mark. A precise recorder does not erase it and does not panic. You take that one measurement again, the same careful way, and see whether the strange reading was just a slip.
Spot the shadow reading to measure again
The same stick's shadow was measured every half hour as the afternoon went on, and the lengths were read off the tape. The shadow should lengthen steadily, but one reading does not fit the climb.
Click the point that does not fit the pattern of the others.
Which readings were measured with precision?
A reading is only useful if it was taken with reasonable precision and logged with its unit. Some readings were made the proper way, reading the finest mark level with the eye and noting the unit. Others were rushed, guessed, or written without a unit, so they cannot be trusted or compared. Sort each one by whether it is a precise, trustworthy record of the shadow and temperature measuring you set out to do.
Decide which readings were measured with reasonable precision
The aim: make precise, trustworthy records of shadow length and temperature. Decide which readings meet that aim.
Claim: A precise reading is taken to the finest mark or digit the tool allows, read level with the scale, and recorded with its unit.
The shadow ended between two marks, so it was read to the nearest millimetre as 14.3 cm.
The digital thermometer showed 21.4 degrees, and 21.4 deg C was logged with its unit.
The shadow looked about a hand long, so 15 was written down with no unit.
The tape was read level with the eye and the mark, giving 30.8 cm to the nearest millimetre.
A temperature was guessed from how warm the day felt, without reading the thermometer.
Decide whether each statement is evidence for the claim, or not.
Why this matters
Measuring with reasonable precision is what makes data worth collecting. When you choose the right unit, read the finest mark or digit carefully, let a digital tool log the value, and repeat the reading to check it, your records can be trusted, compared and built on by anyone. It is the same care a meteorologist, an engineer or a scientist takes whenever a measurement has to be right.
Quick self-check
1. You measure a shadow with a tape and the end falls between 14 and 15 centimetres. How do you record it with reasonable precision?
2. To read the millimetre scale on a ruler or tape correctly, where should your eye be?
3. A digital thermometer shows 21.4 degrees and a second later shows 21.5 degrees. What does the extra digit tell you?
4. Why take the same careful measurement three times and not just once?
5. Your shadow lengths are 30 cm, 25 cm, 20 cm, then 38 cm, then 12 cm. The 38 cm reading does not fit the steady fall. What should you do?