Oct,31--Significant Figures

Significant digits are meaningful digits. More significant digits means more precise.
-The last digit of the measurement is uncertain (because that digit could be one digit higher or one digit lower
-ex. 5.23 then become 5.2, 5.26 then become 5.3)
Ex 1: 9.34 9 and 3 are certain, 4 is uncertain
-The significant figures include all of the certain digits and the first uncertain digitEx 2: 9.34 have 3 significant digits

Rules of counted significant digits in the measurement:
-leading zeros aren’t counted
-Trailing zeros after the decimal point are counted
-Trailing zeros without a decimal point are not counted

Exact numbers
-quantities that are defined as exactly a certain amount (we don’t need to round it)
Rounding rules:-If that digit is ＞5，round up
-if that digit is ＜5，keep it the same
-if that digit is =5, and there are more non-zero digits after the 5 round up
-if that digit is =5, and it ends at the 5 round to make the last digit “Even” (0, 2, 4, 6, 8)

Math Rules (+ and -)(x and /):
 round to the fewest number of decimal places (by position)
*: round to the fewest number significant digits