Chess Champion Mark 6
                (Philidor module)

The Philidor module appeared in 1982/1983. It can be slided easily onto the Chess Champion Mk V:

With this Philidor module the Chess Champion Mk V is changed into the Chess Champion Mark VI.

At the time, this module cost more than half of the price of the Chess Champion Mk V, but the Elo rating of the computer was increased by no more than some 20 points.

In spite of the disappointing quality (or maybe thanks to it) the module is quite rare.