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# 9 When to use the calculator

Despite the list of advantages given, here is a word of warning: a calculator is not a substitute for a brain! Even when you are using your calculator, you will still need to sort out what calculation to do to get the answer to a particular problem. However skilled you are at using your calculator, if you do the wrong sum, you will get the wrong answer. The phrase ‘garbage in, garbage out’ applies just as much to calculators as to computers. Your calculator is just that – a calculator!

It will not replace your number sense either. The skills of estimating answers in your head and knowing when the answer you get is reasonable are even more important when using a calculator. It is very easy to press the wrong key by mistake and you need to be able to tell when you have made an error.

So the calculator is not a substitute for thinking: it is a tool to help you to expand the range of problems that you can tackle. You will need to use it in conjunction with other tools, such as pencil and paper and you will always need to think about what you are doing. The answer from your calculator may be an accurate calculation of what you entered, but you need to use your head to ensure that what you put in was what was needed. You also need to interpret the output from the calculator in the relevant situation.

As you have already seen a calculator often encourages you to use your head as well as your fingers: as in the ‘Guess and Press’ exercise. Here are some more guidelines to help you to use your calculator sensibly.

• Use the calculator for calculations where you would be liable to make a mistake or where it would take a long time to do them in your head and/or with pencil and paper.

• When solving a problem, write down what you are doing on paper and check that you are doing the right calculation for your particular problem.

• Estimate the rough size of your answer, so that if you get something very different you will be alerted to a possible error in your input to the calculator.

• Always check that your input is correct as it appears on the screen and amend it if necessary.

Since checking and estimating are so important in calculator work, you should make sure your estimating skills are up to scratch!

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