The size of the lathe is expressed by stating the length of the bed, and the largest diameter it will swing on centers. The "swing" is found by measuring from the point of the head-stock center to the "ways" on the bed, and multiplying by two. The length of a lathe's bed is the distance the tail-stock will move backward. If accuracy is desired, this measurement should be the distance between the two centers when the tail-stock is pushed backward as far as it will go. The length of the piece the lathe will turn is limited by the distance between its centers.