Significant figures in measurement with error

Someone can explain me what's the rule behind the correct expression of a quantity $K$ with its error $\Delta K$ as $K \pm \Delta K$? They must have the same number of significant figures? Or the error should have in general 1-2 significant figures? For example, if I have:

$$K = 8510.33 \pm 56.97~.$$ This expression is uncorrect? Maybe should be expressed as: $$K= 8510 \pm 57~?$$