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npl.co.uk © NPL Management Ltd, 2019. 12415/0119 Disclaimer Although every effort is made to ensure that the information contained in this brochure is accurate and up to date, NPL does not make any representations or warranties, whether express, implied by law or by statute, as to its accuracy, completeness or reliability. NPL excludes all liabilities arising from the use of this brochure to the fullest extent permissible by law. NPL reserves the right at any time to make changes to the material, or discontinue the brochure, without notice. The NPL name and logo are owned by NPL Management Limited. Any use of any logos must be authorised in writing. The National Physical Laboratory (NPL) develops and maintains the UK’s primary measurement standards, which are used to check the accuracy of instruments used by thousands of other organisations making millions of measurements. Did you know? Accuracy is a qualitative term that describes how close the measurements are to the actual (true) value. Precision describes the spread of these measurements when they are repeated. Resolution is the smallest difference that can be meaningfully distinguished. For example, a change of one in the last place of a digital display. Even when we are precise and accurate, there will still be some uncertainty in our measurements. The challenge for anyone doing measurements – and that is everyone (not just scientists and engineers) – is to assess the uncertainty and make it as small as appropriate for a particular application. For example, you do not need to measure cake ingredients with an uncertainty of millionths of a gram. The difference between ACCURACY & PRECISION We use several words when describing measurement results. This poster should help you understand some of these words. Missed the target centre, and the three attempts were not near each other. Low accuracy and low precision Three attempts were near the target centre, but were not near each other. High accuracy, but low precision Missed the target centre, but the three attempts were near each other. Low accuracy, but high precision Hit the target centre three times! High accuracy and high precision Increasing accuracy Increasing precision

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  • npl.co.uk© NPL Management Ltd, 2019. 12415/0119

    Disclaimer Although every effort is made to ensure that the information contained in this brochure is accurate and up to date, NPL does not make any representations or warranties, whether express, implied by law or by statute, as to its accuracy, completeness or reliability. NPL excludes all liabilities arising from the use of this brochure to the fullest extent permissible by law. NPL reserves the right at any time to make changes to the material, or discontinue the brochure, without notice. The NPL name and logo are owned by NPL Management Limited. Any use of any logos must be authorised in writing.

    The National Physical Laboratory (NPL) develops and maintains the UK’s primary measurement standards, which are used to check the accuracy of instruments used by thousands of other organisations making millions of measurements.

    Did you know?

    Accuracy is a qualitative term that describes how close the measurements are to the actual (true) value.

    Precision describes the spread of these measurements when they are repeated.

    Resolution is the smallest difference that can be meaningfully distinguished. For example, a change of one in the last place of a digital display.

    Even when we are precise and accurate, there will still be some uncertainty in our measurements. The challenge for anyone doing measurements – and that is everyone (not just scientists and engineers) – is to assess the uncertainty and make it as small as appropriate for a particular application. For example, you do not need to measure cake ingredients with an uncertainty of millionths of a gram.

    The difference between ACCURACY & PRECISIONWe use several words when describing measurement results.This poster should help you understand some of these words.

    Missed the target centre, and the three attempts were not near each other.

    Low accuracy and low precision

    Three attempts were near the target centre, but were not near each other.

    High accuracy, but low precision

    Missed the target centre, but the three attempts were near each other.

    Low accuracy, but high precision

    Hit the target centre three times!

    High accuracy and high precision

    Incr

    easi

    ng a

    ccur

    acy

    Increasing precision