  The partition is then removed from the centre of the box, so the molecule is free to travel throughout the box. The partition is inserted into the far right hand side of the box and, maintaining thermal contact, is slowly moved to the centre of the box. Once again, collisions with the molecule exert a pressure on the partition, requiring work to be performed, and the energy from the work is transferred via the molecule to heat in the heat bath. Standard calculations show this requires at least kT  ln 2 work. One expression of what has now become known as “Landauer's principle” is that there are no possible physical implementations of the resetting operation that can do better that this, that is, reset a bit to zero converting less than kT  ln 2 of work into heat.