The precision of a measurement can be stated explicitly by stating the measurement value along with the uncertainty interval
e.g 100cm +/- 1cm
Alternatively precision can be given implicitly by the number of significant digits used for the measurement value. (The term significant digit will be explained in the next section however in the examples below all of the digits are significant digits)
When the precision of a number is given implicitly by the number of significant digits then the uncertainty is taken to be half a unit either side of the least significant digit (this is simply the last digit in the examples below).
(Note when we write a value such as say 17 +/- 0.5 by convention we are actually expressing the range from and including 16.5 up to but not including 17.5 (e.g 16.5 - 17.4999.. )).