Measurements and Calculations
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When you 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.
Record all digits that are certain plus one uncertain digit. ("Certain plus one") all of these digits are called significant digits. A decimal has no bearing on how many significant digits there is, in fact ingnore the decimal.
The Rule Con't:
All the digits in the value are significant digits except for any zeros (0) preceeding the value. (please go over the number below for explaination)
As you can see there are 4 certain digits plus 1 uncertain digit totalling 5 significant digits. The leading zeros have no bearing on the number of significant digit. If the zero's are somewhere after the first significant number, then they count as a significant digit.
Another chart showing the correct way to record measurements:
Counted or Defined Values
Counted or Defined values are exact values. Exact values contain an infinite number of significant digits. Defined values like 1000km/km or 60s/min are example of exact values.
A person can not look at a parking lot and say there is 3 and a half cars parked (otherwise the person with the half car got ripped off). In this case it is a exact value of 3 cars.
As you can see there can only be a exact value when you count.
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