Quite often the uncertainty in measurement is expressed in terms of percentage by putting $$\pm$$ sign before it, e.g., $$250 \pm 1\%$$ etc. If the same instrument is used for measuring different quantities, then smaller the quantity to equal to $$\pm 1$$ mg, then if weigh $$100 \;g$$ on it, the result can be reported as $$100 \pm 0.01\%,$$ and if 1 g is weighed, the result reported will be $$10 \pm 0.1\%$$. Hence, smaller the quantity to be measured, more precise should be the instrument.