How does Wien's Scaling Law unify experimental data in blackbody radiation?

[Narcol2000]

How does Wien's scaling law

<br /> \frac{u(\lambda)}{T^5} = \frac{f(\lambda T)}{\lambda^5T^5}<br />

imply that if \frac{u(\lambda)}{T^5} is plotted as a function of \lambda T, all experimental data will lie on a single curve?

 

[CompuChip]

I don't know anything about the physics here, but it seems obvious to me that if you plot y = u(\lambda)/T^5 versus x = \lambda T then Wien's scaling law tells you that y = f(x) / x^5. So if you take a data point (x', y') and Wiens' law is true, then y' should be (within error) f(x')/(x')^5.