Sensible Accuracy

How Accurate?
Discuss these questions:

Do the clocks' you use keep good time?
Would you notice if a clock gained one second every week?
Is your ruler accurate enough for your mathematics and science lessons?
How, well can you measure?
How, accurately, do you need to measure?

In science it is sometimes important to be very accurate: that is why quartz watches were invented.

But if you are seeing how fast a lake freezes at two degrees of frost, timing to the nearest hour is sufficient: an ordinary clock would do.

Pouring Milk
Britain is changing to the metric system. This means measuring in litres instead of pints.

One housewife argued:

'I have to use a pint of milk in my cooking. One pint is 0.56826 litres, 1 am not going to ask my milkman for 0.56826 litres of milk.'

It is possible to be too accurate. It is false accuracy to say here that a pint is 0.56826 litres. A housewife does not measure the amount of milk she puts in a cup of tea. The difference between 0.56 and 0.57 litres of milk is very small. It is less than the milk in a cup of tea. This difference is too small to affect most cooking recipes. You could not tell the difference between 0.56 and 0.57 litres on most measuring jugs.

False accuracy should be avoided.

Sometimes we need to be more accurate. A car mechanic must set a sparking plug gap correctly. Medicine is measured using 5 ml spoons. To find a sensible answer when converting you must think:

1. How accurate is the original answer?
2. How accurate do I need to be?

Always give an answer which is accurate enough, but not so precise as to be unhelpful.

Changing Units
The questions below are about conversions.

In each case decide whether the given answer is too accurate, sensible or not accurate enough. If the answer is too accurate, write down a sensible answer. If it is not accurate enough, write down a sensible answer using these conversions and a calculator.

*Mathematical Calculations
In mathematics you sometimes have to use or . You must be careful to give a sensible answer. Say whether each of the answers below is too accurate, sensible or not accurate enough. Correct them if you need to.

Other Figures
Sometimes people give figures which are too accurate. It may not be possible to count or measure so accurately. For each example below, say why the figure is too accurate and give a sensible answer.

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