Once a location (usually a station, but not always) has been pegged
it is possible to perform a rotational movement around it, as if it was the centre of a circle or spiral. As most moves in Mornington Crescent are linear, a well-timed pivot can get round obstacles that could not be circumvented in any other way. When performing such a manoeuver, it pays to pay close attention to line velocity
and the current level of helical stress
; if either is excessive, the pivot manoeuver may fail badly. A Crossmead Spiral
or Pettengale Sweep
is a (usually) safer methor to approximate a pivot using standard linear rather than rotational moves, and the hazards of incorrectly executing a Crossmead Spiral are well-documented.