手册里关于ring repeater的一个错误

手册里说：

To set the rotation angle difference between the first and the last copy, use:
/gate/Name_Volume/ring/setAngularSpan x deg

The default angle is 360 deg.

The AngularSpan, the FirstAngle and the RepeatNumber allow one to define the rotation angle difference between two adjacent copies (AngularPitch).

（AngularSpan-FirstAngle）/（RepeatNumber-1）＝ AngularPitch

AngularSpan是difference between the first and the last copy, 这个没有错，但是上面的计算AngularPitch的公式里不应该有FirstAngle。

比如在定义Mosaic的crystal的时候，先用下面的定义没有问题：

/gate/rsector/repeaters/insert ring
/gate/rsector/ring/setFirstAngle 0. deg
/gate/rsector/ring/setAngularSpan -358.705 deg
/gate/rsector/ring/setRepeatNumber 278

为了让第一个crystal有一个angular shift，我改成了这样：

/gate/rsector/repeaters/insert ring
/gate/rsector/ring/setFirstAngle -0.6475 deg
/gate/rsector/ring/setAngularSpan -359.3525 deg
/gate/rsector/ring/setRepeatNumber 278

结果就不对了。最后发现，setFirstAngle增加一个shift之后，setAngularSpan仍然不变，即setAngularSpan是第一个和最后一个crystal的差，而不是最后一个crystal的绝对位置。下面的定义是正确的：

/gate/rsector/repeaters/insert ring
/gate/rsector/ring/setFirstAngle -0.6475 deg
/gate/rsector/ring/setAngularSpan -358.705 deg
/gate/rsector/ring/setRepeatNumber 278