Suppose we made a measurement of 0.0005600.000560,,,there are THREE significant figures but writing the number down as is INVITES error. Alternatively we could use powers of 10...
0.000560-=5.60xx10^-40.000560≡5.60×10−4...to give a number that is a bit more accessible in scientific notation. If you have doubts, plug the numbers into your calculator, and then use them...the calculator will convert them.