The Three Calibers Rule

Keyhand: As far as I know, in WoT PC having a 3xOvermatch does not guarantee penetration but the matter of cases where this is an issue is negligible I would say (probably limited to some mid-tier Derp guns firing AP) since the nominal normalization also becomes larger because of the 2xOvermatch which obviously affects larger calibers as well.

Taken from the wiki:Why else would anyone mention the 2x rule also applies when the shell is 3x when it would 100% pen anyway?