How Did They Build Canal Tunnels in a Straight Line?

How did they build canal tunnels in a straight line using just basic hand tools like pick-axes, shovels, and wheelbarrows? Colin uncovers the 18th Century tricks-of-the-trade used to build Blisworth Tunnel on the Grand Union Canal between Stoke Bruerne and Blisworth. You'll be surprised by the methods used over two hundred years ago and just how easy it is to build a three-kilometer canal tunnel in a straight line.