SR 5th ed. Cyber Implant Weapons

[d20Maverick]

I'm in the process of building a lot of the characters that my group plays, and I wanted to confirm whether the character's builder (who isn't the PC's player) is correct or if HeroLab is. HeroLab requires that cyber-implant weapons installed in cyberlimbs (in this case, a gyro mount and spurs in a cyber arm) are the same grade as the cyberlimb itself. However, I don't see where that is stated in the core rulebook's section on cyber implant weapons (p. 458). Have I missed that rule in another section, or is that an assumption (perfectly reasonable though it may be) that was made during the programming of HeroLab?

If I've missed it, I'd like to find a page reference to point out to the character's builder. I know that I have misunderstood a few things which HeroLab has helped me straighten out, and he has as well, but it's always nice to be able to point out where mistakes were made. Any assistance you guys can offer would be appreciated.