Invented by great theoretician but mediocre player Ernest Mipplington
, this is the standard way of measuring move difficulty. A simple move has HDR 0.2, a typical shunt around 1.2, an average Czukay Manipulation
in the range 3.7 to 4.9. The hardest move ever played occurred in the semi-final of the 1976 World Championship. It took the Andorran Champion (whose name has sadly been lost from Amersham) to Chalk Farm with all the diagonals
closed, six lines quartered
, fifty-two stations bulkheaded
and sixteen more blocked
. It took him almost two hours to work out. The HDR was later found to be 396.5.