3- Measuring Length.

Length is “the distance between two points in a space”.

According to SI units, the length quantity is expressed in meter.

There are several kinds of measuring devices used to measure quantity of length, among others, are as follows.


Tools used

a-   Rule.

b-   Tapes.

c-   Callipers

d-   Vernier callipers.

e-    Micrometre

  • Meter rule (ruler) can be used to measure lengths from millimeters up till meters (The ruler uses cm or mm scale with accuracy of 0.1cm or 1 mm.).
  • Longer lengths can be measured by using tape as dimensions of a room.
Steel ruler

The most common, and the best known, piece of measuring equipment

What is Zero error?

Reducing reading errors

1-   Taking several readings of the subject to be measured can also help to reduce reading errors

2-   Avoid parallax error.


 Parallax error

When using such instruments, parallax error must be avoided.

Always align your eye with the position being measured

Vernier Calliper

  • A Vernier calliper has two main parts, namely outer jaw to measure thickness and inner jaw to measure the diameter of inner part of an object.
  • The accuracy of the Vernier calliper reaches 0.1 mm.
  • Vernier calliper has two jaws, namely fixed jaw and sliding jaw.
  • The fixed jaw has length scale which is called main scale, while the sliding jaw has short scale which is called Vernier scale.


The measurement of a small distance (use of a micrometre screw gauge)

Micrometres are used to measure small distances accurately (has accuracy until 0.01 mm. The screw micrometre is usually used to measure tiny or small objects.)

Reading vernier callipers


Reading micrometer


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