In that case count them. If the count hits 30, bingo.
Activation: east present
Condition: count thislist <= 30
On activation: whatever
would that do it?
Or better 2 trigs
Activation: east present
Condition: true
On activation: eastList1 = count thislist
Activation: east present
Condition: count thislist < eastList1
On activation: whatever
Syntax etc not guaranteed.