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Contents → FOUR-CIRCLE REFERENCE → Cut Points

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The angles -90° and +270° are at the same position on a circle, but if a motor in spec is sitting at 0°, it will move counter-clockwise by 90° to get to the -90° position and clockwise by 270° to get to the +270° position.

By setting a lower cut point for a particular motor, you can choose what value on the circle the four-circle angle calculations will produce. That is, the calculations will place the angle between the lower cut point and that value plus 360°.

Cut points can be set for the θ, χ and φ four-circle angles. For the 2θ angle, the lower cut point is fixed at -180°. For the azimuth-fixed modes, there is pseudo-cut point for the azimuthal angle. If the cut point is less than zero, the calculated azimuth will be between -180° and 0°, otherwise the azimuth will be between 0° and +180°.


The default cut points are shown below.

Angle	Default Cut Point
θ	-180
χ	-180
φ	-180
ψ	0

The macro cuts can be used to set or display the cut points. With no arguments, it displays the current cut points. Two arguments are used to set a single cut point. Four arguments set all cut points.

1.FOURC> cuts

Cut Points:

    th   chi   phi  azimuth
  -180  -180  -180        0

2.FOURC> cuts phi 90

or

3.FOURC> cuts -180 -180 90 0

4.FOURC> 

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