X-Y double-axis gimbal by X axis transferring D could track objects near zenith, has wider tracking region than regular X-Y double-axis gimbal.

偏X-Y双轴式光电跟踪系统可以解决过顶跟踪问题，其跟踪范围与规则X-Y双轴式光电跟踪系统相比有很大提高。

youdao

If you say, "Add the vectors, " I would just add the x to the x and the y to the y and I'm keeping track of what the sum is.

如果你们说 " 将矢量相加 ",我就把同为 x 轴方向的分量相加,同为 y 轴方向的分量相加,然后就能得出这两个矢量的和是多少了

耶鲁公开课 - 基础物理课程节选

Bottom line: To stay on track for retirement, Gen Y is going to have to run a marathon.

FORBES: Are Young Workers On Track For Retirement--Or Smoking Something?