DEC edge connector contact identification
The edge connector contact groups of DEC cards such as FLIP CHIPs on the edge of a hex card are 'numbered' A-F. The groups are often called 'rows' in DEC documentation; the term 'slots' is also used, but this is confusing, because backplanes also have numbered slots for cards, numbered horizontally. The term 'connector' is also seen.
The groups are 'numbered' starting from the top (when the card is installed, vertically), with 'A'; this would be the right-hand edge, when the card is horizontal, with the component side up, and the connector 'fingers' toward the viewer. Shorter cards (quads and duals) use subsets of these, also starting with 'A'.
Within each row, the individual contacts are 'numbered' from the DEC Alphabet; those on the component side are further numbered '1', and those on the solder side (for boards with contacts on both sides - not all do), '2'. I.e. with the board in a horizontal position, as described above, the right-most contact on the top side (i.e. visible) would be identified as 'AA1'.