Zero and Parallax Error
2 Minutes
Zero error and parallax error explained for students to learn how to measure accurately using scales and meters. A short science lesson in English.
- Why measuring tools like tapes and scales must start at zero
- Positive and negative zero errors on weighing machines and meters
- How parallax error happens from misreading the starting point
What this lesson teaches
Zero error and parallax error are two common measurement mistakes that prevent tools like tapes, scales, and meters from giving accurate readings of length, height, or weight. To get correct measurements, the measuring tool must start exactly at zero and the marks must be viewed properly without misjudging the starting point.
What zero error is
A zero error occurs when a measuring device does not start correctly from the zero mark. Tools like measuring tapes, weighing machines, and fuel meters are designed to begin at zero before taking any measurement. If a weighing machine pointer rests above zero before someone steps on it, the reading will show more than their actual weight, and if it rests below zero, it will show less. Petrol stations also instruct customers to verify that the meter begins at zero to avoid inaccurate fuel readings.
Positive and negative zero errors
Zero errors are divided into positive and negative errors based on where the starting point is placed:
- A positive error happens when a measurement is taken by placing the object before the zero mark.
- Placing the zero point further back causes the measured length of the object to appear greater.
- A negative error happens when a measurement is taken by placing the object after the zero mark.
- Placing the zero point further forward causes the measured length of the object to appear less.
How parallax error occurs
Parallax error happens when an observer reads the measurements on an instrument incorrectly. For example, when measuring the length of a drawn straight line, looking at the ruler can make the line seem to begin at zero when it really does not. The line may actually start slightly ahead of or behind the zero mark. This minor viewing mistake leads to an inaccurate measurement because the true starting position is misjudged.
How to prevent measurement errors
Accurate measurements of length, height, and weight require checking both the instrument and the way it is read:
- Check that the measuring tool, weighing machine, or meter indicator starts precisely at zero before measuring.
- Ensure the object being measured is placed directly at zero rather than before or after it.
- Look carefully at the markings so that visual mistakes do not shift the apparent starting point.
- Avoid both zero error and parallax error to ensure that the final reading is correct.