the fx-39 say no more!
this was a real trooper of a machine back in
1978 when it
came out. similar in look but somewhat improved over the fx-29.
the 39 had an inv button which means a
lot more could be accommodated on the keyboard (was this the first casio
with an inv button?). parentheses are also
here, not present on the earlier 29, and to a limited extent
casio had also figured out a neat trick was to share
the exp button with pi. when entering
numbers exp would enter the exponent, when
operating with numbers the same button would recall pi.
was inverting hms display. a decimal hour value could be converted back to
hours, minutes and seconds. displayed in the, now familiar, casio way with
a small upper digit degree sign.
an undocumented feature was that the
operator keys (+, -, *, /) implemented combinations, permutations and
polar/rectangular conversion when prefixed with the inv button exactly like the later fx-120. i have no
idea why this was never documented. perhaps they forgot to put the legends
on the front panel.
this model would suffer the sticky button