Rules for Determining Significant Figures are critical



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Rules for Determining Significant Figures

Significant figures are critical when reporting scientific data because they give the reader an idea of how accurately you could actually measure/report your data.

**The data is only as reliable as your least significant/accurate measurement
1) ALL non-zero numbers (1,2,3,4,5,6,7,8,9) are ALWAYS significant.

2) ALL zeroes between non-zero numbers are ALWAYSsignificant.

3) ALL zeroes which are SIMULTANEOUSLY to the right of the decimal point AND

at the end of the number are ALWAYS significant.(see Atlantic & Pacific rule below)

4) ALL zeroes which are to the left of a written decimal point and are in a number >= 10

are ALWAYS significant.. (see Atlantic & Pacific rule below)



**A helpful way to check rules 3 and 4 is to write the number in scientific notation.

If you can/must get rid of the zeroes, then they are NOT significant.
The Atlantic/Pacific Rule for Determining Significant Figures
1) look for the Presence, or Absence, of a decimal point

- this will tell you which side to start counting from Pacific: left Atlantic: right




Pacific Atlantic

2) if there is a decimal point (Presence) you start counting from the left side of the number

- starting from the very left side of the number

- look for the first non-zero number

- count the first non-zero number and every number (0-9) after that

- example: 0.00030

- because there is a decimal point (Present), we start from the left side of the number
left →0.00030, and look for the first non-zero number 0.00030

- count that number and every number after that regardless of what the number is (0-9)

- in this case there are 2 significant figures - 0.00030
3) if there is not a decimal point (Absence) you start counting from the right side of the number

- starting from the very right side of the number, look for the first non-zero number

- count the first non-zero number and every number (0-9) after that

- example: 789000

- because there is no decimal point (Absent), we start from the right side of the number
789000 ← right, and look for the first non-zero number 789000

- count that number and every number after that regardless of what the number is (0-9)



- in this case there are 3 significant figures - 789000

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