That means that the last two digits of the number 1.00005129 are uncertain. For example, they measured 1.00005129c, but maybe their uncertainty is +-0.0000001c

That means that the last two digits of the number 1.00005129 are uncertain. For example, they measured 1.00005129c, but maybe their uncertainty is +-0.0000001c. The last digits are unreliable, but are the measurements they got EDIT: below, its claimed that those digits ARE the uncertainty. That quite possibly is it; my answer is from what i remember from uncertainty in my 1st year Physics course.