In physics what is the percentage uncertainty in a measurement of say 15cm,using a metre rule??

[Peter Check]

I am really confused about measuring the % uncerainty using a scale like a metre rule( I know its something divided by the reading which, here is 16cm). If i measure 16 cm, do I get he numerator as the smallest division or half the smallest division? In a metre rule, I know the smallest division is .1cm or 1mm, so is the numerator +/- 1mm or +/- 0.5mm ??

 

[Haider2011]

.1/16 *100