# why do we need standard units for measurement

What is a measurement? Measurement maybe defined as a reference for the determination of quantities and qualities. It is a repetition of a unit amount that maintains its size, within an allowable range of error, no matter which instrument is used and no matter what person or thing being measured is. Why is a standardisation of measurements necessary? Let s suppose you were blind folded and you had to describe something. How would you do it? If you know a set of specifications of object or person, you will be able to describe it, or if some one speaks about it, you will understand easily. But if you don t know the specifications, it will be very difficult to describe or even form an opinion about it. A standardisation of measurements is necessary because you need a consistent way to communicate size, shape, mass, time, energy, power, speed. What are the different systems of measurements? There are essentially three systems of measurements used all over the world. The Imperial or the English System, the US Customary Units and the Metric system. The Metric System has been adopted as the Standard International Units of Measurement System in most countries. The Metric system has been adopted because the conversion from lower values to higher values, and the reverse is possible easily and as multiples.

When did the Metric System come into use? The Metric System came to be in use around the French Revolution, in 1799. The definitions of the base units have been modified since the Metre Convention, in 1875. In 1960, these were standardised as the International System of Units. What are the Standard International System of Units? Weight : Length of Distance : centimetres, metres and kilometres

Fluid Mass Measurements : Temperature : Time : seconds, minutes and hour Electric Current : Amount of Substance : Luminosity : A ruler is a foot long and usually has inch and centimeter marks. A meter stick is a meter long and usually has foot, inches, and centimeter marks. Weighing Scales always use pounds, kilograms, ounces. Measuring cups are normally marked in cups and ounces. Non standard measurements use approximate references like cubits, spans etc. Measure a square or rectangular object like a table, or your friend s height. First use your arm and then use a measuring tape. Note down how the measurement changes when you use a different hand to measure. Now you will understand why a Standard Unit of Measurement is required.

What are standard and non-standard units? Standard units are the units we usually use to measure the weight, length or capacity of objects. The standard (metric) units that would be discussed at primary school would include: grams and kilograms, centimetres, metres and kilometres, millilitres and litres (though children also learn about in Year 5 maths). Non-standard units are used by children in Foundation Stage (nursery and Reception) and Year 1, to introduce very young children to the concept of measuring without them having to read any scales. Reading scales of any kind is a challenging skill in itself, so the idea of non-standard measures is to focus the child on the concept of heavier, lighter, longer, shorter, etc. before they go move onto the next step of measuring using standard units. To measure weight, a child might be given a lever balance (like the one below), a lump of plasticine and lots of equal-sized blocks. They may be asked to work out how many blocks weigh the same as the lump of plasticine. They may then be given another object, such as a pencil, and asked to work out how many blocks weigh the same as the pencil.

If they use fewer blocks this time, they should be able to understand the concept of the plasticine weighing more than the pencil and be able to put this into a sentence verbally, for example: The plasticine is heavier than the pencil. P P P POR P P P The pencil is lighter than the plasticine. Another example of using non-standard units would be to use hand span to measure length. For example: a child might be asked to measure the length of their table using their hand span. They would then record how many hand spans the table was and record this. They might then be asked to measure the length of a book. They would need to express what they had learnt verbally with statements such as: The book is shorter than the table. P P P P P P P POR P P P P The table is longer than the book. Children might also be asked to measure in various containers by using small containers to measure amounts of liquid. Children would be expected to use standard units of measurement in Year 2, where they would learn which equipment and units were appropriate for different objects. For example: they would need to know that you would measure the length of a pencil in centimetres using a ruler, the weight of a bag of sugar in kilograms using weighing scales and the capacity of some water in litres using a measuring jug.

By Year 3 children would continue to do practical work on measuring as in Year 2 as well as problem-solving on paper, and they would also start to learn about the relationship between units of measurement. They would need to know the following facts: In Year 4 they would need to be able to. For example: they would need to know that 1. 3 litres is the same as 1300ml, or 150cm is the same as 1. 5m. They would continue to do practical measuring activities and problem-solving. They may come across problems where they have to convert units of measurement in order to work out the answer. For example: I am 1. 3m tall. My baby sister is 86cm tall. How much taller am I than my sister? Children would continue this kind of problem-solving in Year 5 and would most likely be required to solve measures problems involving (addition, subtraction, multiplication and division). In Year 6, they would again continue this kind of problem-solving, but would be required to convert between units using decimals to three places, for example: change 6. 283 kilograms to 6283 grams and vice versa.

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