ETC Congo Family v6.4.0 - Manual (Page 471)

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You can use the numbering functions that allow you to select every 2nd, 3rd or Nth together
with the random function.
Function Soft Key Feedback
Random 2nd [RANDOM] & [SELECT_2nd] Every random
2nd is selected.
Random 3rd [RANDOM] & [SELECT_3rd] Every random
3rd is selected.
Random Nth [RANDOM] & [SELECT_Nth] Every random
Nth is selected.