no measure is ever exact, some error is always involved therefore every answer in science has some uncertainty 

*using sigfigs we can tell what is certain in a measurement and what is uncertain 

• non-zero digits are always significant 

-number 1-9 are sig 

- 14.3g -- 3 sig figs 

14.378g 5 sig figs 

14g 2 sigfigs 

• leading zeros are never significant, they only old place

-0.67 -- 2 sig figs 

• confined zeros between 2 non-zero numbers are always significant 

-3208 -- 4 sigfigs 

• trailing 0 @ the end of a # are oly significant if they contain decimals or an over bar 

-30.0 -- 2 sigfigs 

1. do the calculation

2. round answer to the least number of sigfigs of the numbers used (2 sigfigs*4sigs, use 2) 

24.01cm*17cm = 408.17 = 410cm 

Adding & Subtracting 

1. Do the calculation

2. Round your answer to the same # of decimal places as in the number with the least number of decimal places 

-184.2g + 2.324g = 186.524 = 186.5g

-<5 - drop & leave last sigfig alone 

--34.721 to 3 sigfigs = 34.7

->5 - round up the last fig 

--401.7 to 3 sigfigs = 402 

-no non-zero digits following drop the 5, look at the last sigfig, if last sigfig is odd, round up - if even, round down 

--172.5 = 172 

--0.3555 = .356 

*0 is even