If the uncertainty associated with a value is not specified , It is assumed to be +- 1 in final digit. so absolute uncertainty implied by this number is +- 0.1mm
(2.0mm +- 0.1 mm )
given length = 2.0mm
scale is divided by one unit = 0.1 mm
uncertainty is measure = +- 0.1
value become ( 2.0 +- 0.1)
( 3 , 1.9)