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 manœuvre, it pays to pay close attention to
line velocity and the current level of
helical stress; if either is excessive, the pivot manœuvre may fail badly. A
Crossmead Spiral or
Pettengale Sweep is usually a safer method to approximate a pivot using standard linear rather than rotational moves, and even a Crossmead Spiral carries several well-documented hazards if not executed correctly.
[SM]
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