Validation of submitted variable value by old value of same variable

How to validate submitted variable value with old value.

Let’s consider we have variable named: amount. Lets set amount = 100 and complete user task. I want to know that how to handle gateway condition (amount > old amount) without creating oldAmount variable. I mean how to know if amount field changed since second cycle? Is there a way to intercept before saving submitted variables to engine?

I’m not exactly sure what you’re trying to accomplish and why you want to avoid creating a second variable.