@Frank:
The Speak&Spell and Speak&Math are the same inside. The only differences are the touch panel and what they are programmed to say. The general design of the circuit board went through a few revisions over the 30 years or so the S&S was in production. So you may see a difference between the circuit board of a SPell and a Math, but that has more to do with the revision # than the differences between a Math & Spell.