I was driving through the Mersey tunnel the other day (I rarely take the "Ferry 'cross the Mersey" these days - they will insist on playing that Gerry and the Pacemakers record on it all the time).
To reduce the steepness of the incline, the road tunnel curves around quite a lot. I noticed that, once you have the steering wheel on the correct "lock", you don't have to move it again, so the tunnel curve must be the arc of a circle. But the centre of the circle must be out there somewhere under all that rock. So, my question is:- How do you draw a circle (or part thereof), when you can't get to the centre? Mike Shaw Wirral, UK 53' 22" N 03' 02" W
