How do I validate the value of previous fields in SSRS

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SSRS-2008

I have an RDL that has three fields that show the days students have been absent.

I need include code that checks to see if the value entered in the second field is more than the value entered in the first field and the value in the third field is greater than the value in the second field. I also need the value of the third field to not exceed 500.

So, if a teacher enters 10 days in the first student absence field, and 2 (or a value less than 10) in the second or third student absence field, a message displays or something displays to alert the teacher that she or he can't enter values less than the first value.

Can I do this with an IIF? If so, can someone include an example

What I have tried:

Google search, MSDN blog and website