Programming with the Radio Shack EC-4004

[damaltor]

You are right about the 3600p. It has a different housing though than the 3500 and the EC-4004.

Also, there is the fx-2700p:
http://casio.ledudu.com/pockets.asp?type=202&lg=eng
It is almost identical to the 3500p, but for example the two function keys on the left side of the keyboard are slightly different. It also has the 38 steps in 2 programs.