Making measurements, Measuring, Length

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Length

In the previous section we talked about the metric system, and used the units of length to show how the different prefixes relate to each other - such as kilo-, deci-, centi- and milli-.

Floor layers use millimetres for most measurements. However, this hasn't always been the case - see 'Understanding measurements' in the unit Planning and costing for more details on the different units of measure that are used in floor laying.

Audio for slide 2 (mp3 |6|KB)

In cases where thicknesses of less than a millimetre are used, such as when manufacturers state the thickness of a flooring product's wear layer, the unit of measure often used is the micrometre.

One micrometre is 1/1,000,000 (one millionth) of a metre, or 1/1,000 (one thousandth) of a millimetre. Its symbol is ' µm', which is sometimes written as 'um'.

Audio for slide 3 (mp3 |6|KB)

Many people prefer to use the old fashioned term micron instead of micrometre.

This is designed to avoid confusion with the measuring device called the micrometer, although strictly speaking 'micron' is no longer officially recognised as a term under the SI system.

In practice, micrometres are often expressed as millimetres to several decimal places. For example, 500 µm might simply be referred to as 0.5 mm, and 50 µm would be 0.05 mm.

Audio for slide 4 (mp3 |6|KB)

Measuring devices

The most common general-purpose measuring device is the tape measure.

Spring loaded retractable tape measures range in length from tiny 1 metre tapes to the standard 7 to 8 metre tradesperson's tape.

Audio for slide 5 (mp3 |6|KB)

When you look closely at the end of a normal retractable tape, you'll notice that the steel hook is secured with rivets, with a bit of play in the holes allowing it to move back and forth.

The amount of movement allowed is the same as the thickness of the hook.

Its purpose is to compensate for the hook thickness when you either push the tape up against an object for an inside measurement or hook it over the object for an outside measurement.

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Other common measuring devices are as follows:

Steel rule - very rugged, good for fine measurements, able to be used as a straight edge.

Audio for slide 7 (mp3 |6|KB)

Vernier caliper - used for measuring thicknesses and diameters very precisely, in some cases to an accuracy of 10 micrometres, or 0.01 mm.

Audio for slide 8 (mp3 |6|KB)

Laser distance meter - measures digitally with a laser beam; can be either hand held or combined with a laser level.

Learning activity

Audio 9 (mp3 |6|KB)

Below are five segments of a tape measure, together with an arrow pointing to a particular length. See if you can read the correct length in millimetres for each one.

Don't be fooled - some of these are harder than they look! Remember, you'll need to take into account the units of measure, and on two of the segments, the previous markings on the left hand side that aren't visible.

This is good practice for the times when you're actually using a tape measure on the job, especially when you're measuring long lengths. It takes concentration to read off the correct measurement without misreading the position of the graduations on the tape.

Enter your answers in the cells on the right hand side, and click on the 'Check your answer' button for each one as you work through.

Ruler	Length indicated	Unit of measure
	2200	mm
	3110	mm
	7328	mm
	1780	mm
	4585	mm

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Unit: Making measurements

MSAPMOPS101A: Make measurements

Section 2: Measuring

Length

Measuring devices

Learning activity