All status data that refer to the spindle are combined in the module SSP. The
individual variables are defined as arrays where the row index is the number of the
spindle (assigned to the current channel). The spindle can be identified by reading
the variables "name" or "index" in the same module with the respective row index.
The number of spindles can be read from "numSpindles" in the module Y in the
area C. （以上是DoconCD里边的表述）

首先说一下，这个参数我也没怎么用，理解大多来源于DoconCD，所以上边直接贴出了原话，避免理解有误产生的偏差。接下来，探讨一下该问题，说说我的理解，也欢迎大能们参与讨论并指证错误。

row index是主轴号，即第几主轴，从参数numSpindles里边可以读出，我的理解是MD35000你标注了多少，这里就是多少。area C对应area N的不同即area C有多个通道，所以我觉得area index应该是通道几。