Siemens SINUMERIK 828D Programming Manual page 445

System variables
The following system variables can be used in conjunction with the channel axis identifier of
the leading link axis:
System variables
$AA_LEAD_SP
$AA_LEAD_SV
If these system variables are updated by the home NCU of the master axis, the new values
are also transferred to any other NCUs, which wish to control slave axes as a function of this
master axis.
References:
Function Manual, Extended Functions; Multiple Operator Panels and NCUs (B3)
Fundamentals
Programming Manual, 07/2010, 6FC5398-1BP40-0BA0
Significance
Simulated master value - position
Simulated master value - velocity
Other information
15.1 Axes
445