How does accuracy differ from precision?

Accuracy is how close a measurement is to a generally accepted value. Precision is how many digits the measurement is.

My weight is 160 lbs, generally accepted as true.

My to scales recoreded my weight as 164lbs, and as 144.432 lbs.
The most accurate was 164, but the most precise was the 144.432 lbs.

what about

Why must a calculated answear generally be rounded? and how many siginificant figures must you round an answear to when performing multiplication or division?