"True at 10x magnification"??? What does that mean?

"kmd1984"Hi,

I got a new scope and in the manual it says that it is "True" at 10x magnification. What does that mean, and how does that effect me with every day shooting?! Do I need to Zero the scope at 10x magnification? I believe not, but I did it anyway. 

thanks,

Kmd
Mil dots are often used for ranging targets. It is important to know (in a second focal plane scope) at what magnification a the distance between two mil dots really is exactly one mil.