Reading instruments – scale division and parallax error
Integrated ScienceScientific Skills & MeasurementAges 11–12
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Sign in to playPractise reading six instruments with analogue scales: a liquid-in-glass thermometer, a newton meter, a measuring cylinder, a ruler, an analogue stopwatch and an analogue ammeter. Each reading uses a random scale and value: students first work out the value of one scale division, then enter the reading with its unit and get feedback on the value, unit, number of digits, meniscus and the parallax error caused by looking from an angle.
Lesson: Using measuring instruments: scale division (resolution), range, eye position and recording readings
What it shows
Reading an instrument correctly starts with the value of one scale division, found from the difference between two numbered marks divided by the number of intervals between them. A reading is recorded to the nearest mark, with the correct unit and number of digits. The eye must be level with the mark to avoid parallax error, and water in a measuring cylinder is read at the bottom of the meniscus. The simulation models parallax as a shift of the apparent reading in proportion to how far the eye is off level, up to about one division.
How to use
Choose an Instrument and press New reading to get a random scale and value. In Step 1, enter the Scale division and press Check. In Step 2, enter the Reading, choose a unit and press Check. Drag the Eye position slider to see the pointer or liquid level shift against the marks; the side view draws the line of sight. Use Show answer when stuck.
Parameters you can change
- Instrument Liquid-in-glass thermometer, Newton meter, Measuring cylinder, Ruler, Analogue stopwatch, Analogue ammeter
- Parallax error (Eye position slider)
- Show reading tips
Questions to explore
- Why should you work out the scale division before taking a reading?
- If your eye is above the water level in a measuring cylinder, is the reading too high or too low?
- Why do good analogue ammeters have a mirror strip under the scale?
