Measure
&
Estimate

Now when people wanted to measure things

in a way that lots of people could understand,

they obviously had to agree on some units to measure things by,

units of distance and weight and volume.

Now people in places far away from each other

would still measure things using different units,

but as it became easier for people to travel to far away places,

most people ended up using decimal units most of the time.

Counting things in tens and hundreds and thousands makes calculations easy,

and also means that it is possible to measure

very large things to very small things very precisely,

in a way that is easy to imagine.

But for everyday, people usually just want a few standard weights and sizes to work with.

They use round numbers,

close to the nearest ten or hundred or thousand.

And being close but not exact isn't always wrong,

it is sometimes close enough.

If you are weighing potatoes you don't need the answer to the nearest gram.

if you are running a cross country race you don’t need to know the exact number of cms.

So people still use fractions for everyday,

they mix fractions and metric,

say half a meter instead of 50cms for example.

But there are also times when they do need to be more exact,

like the weight of ingredients when baking a cake,

or the length of a pair of trousers.

Estimates don't always do.

And estimates can sometimes be confusing,

especially when things change shape.

A piece of string is the same length, even when it's rolled up into a ball,

And a ball of sponge doesn't weigh the same as a ball of wood or steel the same size,

and a litre can come in all sorts of different shaped containers,

look at the different shapes of bottles of stuff on the shelves of a supermarket.

But working with round numbers can still be useful

even when working with accurate numbers

because they help to keep track of values when using a calculator.

It's useful to make sure that the calculator has been given the right orders,

or to check that the decimal point in a calculator answer is in the right place.

It's always good to let the machine know who's the boss

Fractions can be really useful to work with.

Before Scotland started using grams and kilograms

they used what was known as the imperial system,

where they used a standard weight of one pound, written lb,

made up of 16 ounces, written oz,

as sixteen is a very useful number for sharing and trading.

With weights of just 1oz, 2oz, 4oz, and 8oz,

it was possible for scales to weigh all the different ounces up to a pound,

and add 1lb and 2lb weights and it was possible to go all the way up to 4lb.

Of course, rather than use four weights to make 15oz

traders would put a 1lb weight on one side of the scale and 1oz on the other.

They would use their scales like equations, or vice versa.

But those old ways of measuring haven't completely vanished,

it's still possible to find measurements that were used before metric.

There are road signs and markers like milestones,

using the distance measure of a mile,

made up of 1760 yards.

Liquid volumes were measured in pints and gallons,

eight pints or four quarts to a gallon,

and you can still see the volume measured in pints

written on milk containers.

Anyway, no matter what the units of measure, in the world

it's still the same distance or area

or the same amount of stuff.

It's just a different way to measure it.