Loop Through Subform Instances

I'm very new to Javascripts and Livecycle,

I have 4 fields (field1.rawValue, field2.rawValue, field3.rawValue & field4.rawValue wrapped in Subform1.  I'm attempting to sum values entered in fields 1, 2, & 3 into field 4 with the following script.

var myFields = field1.field2.field3.resolveNodes("Subform1[*]");

var sum = 0.0

for (var i = 0; i < myFields.length; i++) {

sum += myFields.item(i).field4.rawValue;

}

this.rawValue = sum;

When a new instance is added field4(1) should be the sum of field4(0) + field(1) + field2(1) + field3(1).

Thanks,