Validation of Arrays in Product Builder

Does anyone know where I can get some documentation or help regarding post field validation of Arrays in a product model. The user guides only briefly touch on both arrays and validation in isolation and only at the modelling variable level. What im trying to do is validate an entry in a quantity field of a 6x3 array. If there is a quantity entered then I want to do some multiplication of the qty field and a rate per hour field to calculate hours. I figure there are a couple of areas for validation: 1. in the modelling variable field only it looks like Ill need to code it to make it happen from here as syntax is killing me when using the rule wizard and multiple indexes OR 2. in the variable grouping against the array, only it doesnt seem to want to work from here for some reason. I should note that there will not always be an entry in all 6 rows which will also need some validation but I figure if I can get answers for this problem the same rules will apply to the array validation. Hoping someone may be able to point me in the right direction.