This calculator is undoubtedly the rarest in my collection. In fact, there is no other known example of it and until I acquired mine in 2019, there was no other photo of it than the one in the 1975 Casio presentation brochure.
 
This calculator features the same technology as the other machines in the FORTRAN series. It is exceptional because it has 256 program steps and also 15 independent program areas.
 Unfortunately, mine doesn't work perfectly. When I enter a program, it very quickly loses the first instructions.