What Am I Missing (HP-71B)

[Gerson W. Barbosa]

10 OPTION BASE 0
20 DIM A(1), B(1)
30 MAT INPUT A,B
40 DISP DOT(A,B)

Or

40 DISP A(0)*B(0)+A(1)*B(1)

if no Math ROM.

But this doesn't answer your question, I fear.