The recent "valency interaction formula" VIF pictures of molecules look like amplified structural formulas. Yet, from the VIF, on the basis of recent theory of structural covariance which is more general than any symmetry principles, with the pictorial VIF rules, one obtains directly the MO energy level patterns and the HOMO, LUMO types. Whereas Lewis-Langmuir datives and Pauling valence-bonds are no longer adequate for many molecules, VIF’s still apply. In the present paper, the VIF as a "chemist’s tool", enabling chemical deductions on the blackboard, is examined vis-a-vis nonorthogonality of AO bases, strengths of valency interaction lines, and electronegativity differences and compared with the implications of MO energy level computer results using extended Huckel theory (EHT) and Gaussian STO-3G through 6-31G**. Main group hydrides and many species are treated, noting how comparison of "iso-VIF" species is more useful than the conventional look at isoelectronic cases. St is further shown that by the subtraction of an invariant quantity, computer-obtained MO levels can be identified with respect to the nonbonding, bonding, and antibonding natures of each MO directly.