The Hasselblad 2-Way Expose Cable for the Hasselblad ELX Camera provides electronic communication between the camera and digital back (allows for tethered capture from the computer).
The two way cable allows for two way communication which lets you shoot from either the shutter release on the camera or capture from the computer.
Note:
Hasselblad digital backs also require an Adapter Plate to complete the system - sold separately unless you purchase an Adapter Plate Kit which contains both the Plate and Cable.