A. When corresponding wheels on opposite sides of the engine on
different axes are not spaced equally apart; where the axle of any wheel
is not at a right angle to the center line from front to rear of engine,
so they do not run square on the rails, or where the space between the
axle centers on opposite sides is not equal. This is sometimes indicated
by unequal flange wear and should be reported at once. Wheels are out of
quarter when the crank pin in one wheel is not exactly 90 degrees or one
quarter of a turn from the pin in the wheels on the other end of the
same axle. This is usually caused by slipping the engine with sand on
one rail only and the condition of engine should be reported at once.