Significant figures

·       Atlantic (numbers without a period): Start counting from right with first significant figure (other than Zero).  Examples

1,207=  4

2050 =  3

 200  =  1

·        Pacific (numbers with a period): Start counting from left with first significant figure (other than Zero) and count All numbers to the right after the first.    Examples

2,076.9  = 5

   20.50  = 4

   0.020  =  2

http://www.rpi.edu/dept/phys/Dept2/APPhys1/sigfigs/sigfig/flowchart.gif

For those of you who enjoy flowcharts, this one covers the bases

Is the number defined or counted?

- Defined means set up by a ratio, such as 3:1.  Counted means counted.  The purpose of this step is to weed out numbers like 12 in a dozen or 2 in a pair.  The number of significant digits in these numbers doesn't factor in to the final count so they are classified as unlimited. 

- Numbers that aren't defined or counted are measurements from some sort of equipment.  In your labs, there are specific rules that are different from device to device for counting them.

- Numbers that aren't defined or counted are numbers from the problem.

Does the number have a decimal point?

- If it does there are specific rules in further steps.  If it doesn't . . .

Are trailing zeros present?

- Trailing zeros means numbers after the first nonzero number. 

- In 2,000,000 there is 1 significant digit, the 2.  The zeros are trailing zeros.

Are leading zeros present?

- Leading zeros means numbers between the decimal point and the first nonzero number.

- In 0.0000000035 there are 2 significant digits, the 3 and 5.  The zeros are leading zeros

1.  Not a zero?  It's significant.

2.  Zero between two non zeros (Sandwich zero).  It's significant.        707      1001       2012

3.  Zero after a non zero and after a decimal point?  It's significant.  1.050    0.0530    200.00

4.  Counted or a conversion? It's infinitely significant.

1.  If a zero left is to the left of a nonzero?  It's insignificant.  This is called dangling left

0.0000419                 

0.00315                    

0.04

2.  If a zero is to the right of a nonzero and before a decimal point?  It's insignificant.  This is called dangling right.

4900                          

45,000                      

2,501,000