Certain+&+Uncertain+Digits,+Defined+Numbers+and+Accuracy+&+Precision

=​Accurate&Precise, Certain&Uncertain ​Digits and Defined Numbers= Definitions: **Accrurate measurement** a measurement that is close to the correct or acceped value.
 * Precise measurement** the higher **number of significant figures**, the more precise a measurement.

In science, enginerring, industry and statistics, **accuracy** is the degree of conformity of a measured or calculated quantity to its actual, nominal, absolute value.
 * Precision** characterises the degree of mutual agreement or repeatability among a series of individual results..

In summary, if a measurement is close to the correct number, it's accurate, no matter how many significant figures it has. If a measurement has higher number of significant figures, and it may be not close to the actual result, it's precise. So, the results of calculations or measurement can be accurate but not precise or precise but not accurate. Therefore, a calculation or measurement is called //**valid**// if it is both accurate and precise.

Examples: The correct length of a comic book is 30.61200cm. =Certain&Uncertain Digits= When we are talking about how certain you are about a measurement, this is called the degree of certainty or uncertainty. All measurements taken have some degree of certainty so scientist around the world have reached a international agreement about the correct way to record measurements. Remember:** The last digit of a measurement is uncertain digit.
 * A measurement of 30.6cm is accurate but not very precise.
 * If a measurement is 30.58169cm, it's precise but not accurate.
 * If a measurement is given as 30. 61201cm, it's accurate and precise.
 * If a measurement is 40.3cm, it's not accurate and nor precise.
 * The rule: Certain digits + first uncertain digit = the number of significant figures ( certain plus one)

Example: Measurement 50.28cm (5), (0) and (2) are certain digits and (8) is uncertain digit //( Figure1 )//

===[[image:file:///D:/DOCUME~1/zm/LOCALS~1/Temp/GBHCS1TB]9GVU[W%25I[O3%252U.jpg]]=== ​ //Figure 1// //Figure 2// Measurement 32 Cm3 can be written. (3) is certain digit and (2) is uncertain digit. //( Figure 2)//

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=Defined Numbers= The conversation factors (like 1h=60min) are used to define an exact relationship between two things, so that the numbers involved are assumed to be **perfect**. of defined numbers: 1kg=1000g 1L=1000mL 1m=100cm 1km=1000m Defined numbers are ruled by the scientists. We cannot change it randomly. They are formulas when we change one unit into another type of unit.