See the issue with your code is right([reference], 3) will return the last 3 characters of the [reference], what you want to do is get the digits after some point in your string correct?

So what you can do you can subtract the length of the string which is constant, for example, your [refernce] contains a string of length n, out of which first 5 is constant for and you want values post 5, so what you can use is

Right([Reference],Len([orderReference])-5)