<s>
The	O
HP-65	B-Device
is	O
the	O
first	O
magnetic	O
card-programmable	O
handheld	O
calculator	O
.	O
</s>
<s>
Like	O
all	O
Hewlett-Packard	O
calculators	O
of	O
the	O
era	O
and	O
most	O
since	O
,	O
the	O
HP-65	B-Device
used	O
Reverse	O
Polish	O
Notation	O
(	O
RPN	O
)	O
and	O
a	O
four-level	O
automatic	O
operand	O
stack	B-Application
.	O
</s>
<s>
The	O
HP-65	B-Device
introduced	O
the	O
"	O
tall	O
"	O
,	O
trapezoid-shaped	O
keys	O
that	O
would	O
become	O
iconic	O
for	O
many	O
generations	O
of	O
HP	O
calculators	O
.	O
</s>
<s>
The	O
HP-65	B-Device
was	O
one	O
of	O
the	O
first	O
calculators	O
to	O
include	O
a	O
base	O
conversion	O
function	O
,	O
although	O
it	O
only	O
supported	O
octal	O
(	O
base	O
8	O
)	O
conversion	O
.	O
</s>
<s>
The	O
HP-65	B-Device
had	O
a	O
program	O
memory	O
for	O
up	O
to	O
100	O
instructions	O
of	O
6	O
bits	O
which	O
included	O
subroutine	O
calls	O
and	O
conditional	O
branching	O
based	O
on	O
comparison	O
of	O
x	O
and	O
y	O
registers	O
.	O
</s>
<s>
While	O
reversing	O
the	O
card	O
to	O
store	O
a	O
second	O
program	O
was	O
possible	O
,	O
it	O
was	O
officially	O
discouraged	O
(	O
unlike	O
in	O
later	O
models	O
such	O
as	O
the	O
HP-67	B-Device
)	O
because	O
the	O
other	O
half	O
of	O
the	O
card	O
was	O
touched	O
by	O
the	O
rubber	O
wheel	O
during	O
transport	O
,	O
causing	O
extra	O
abrasion	O
.	O
</s>
<s>
The	O
HP-65	B-Device
had	O
an	O
issue/design	O
flaw	O
whereby	O
storage	O
register	O
R9	O
was	O
corrupted	O
whenever	O
the	O
user	O
(	O
or	O
program	O
)	O
executed	O
trigonometric	O
functions	O
or	O
performed	O
comparison	O
tests	O
;	O
this	O
kind	O
of	O
issue	O
was	O
common	O
in	O
many	O
early	O
calculators	O
,	O
caused	O
by	O
a	O
lack	O
of	O
memory	O
due	O
to	O
cost	O
,	O
power	O
,	O
or	O
size	O
considerations	O
.	O
</s>
<s>
Since	O
the	O
limitation	O
was	O
intended	O
from	O
the	O
beginning	O
and	O
documented	O
in	O
the	O
manual	O
,	O
it	O
is	O
not	O
,	O
strictly	O
speaking	O
,	O
a	O
bug	B-Error_Name
.	O
</s>
<s>
During	O
the	O
1975	O
Apollo-Soyuz	O
Test	O
Project	O
,	O
the	O
HP-65	B-Device
became	O
the	O
first	O
programmable	B-Application
handheld	O
calculator	O
in	O
outer	O
space	O
.	O
</s>
<s>
Two	O
HP-65s	B-Device
were	O
carried	O
on	O
board	O
the	O
Apollo	O
spacecraft	O
.	O
</s>
<s>
Calculation	O
of	O
parameters	O
for	O
the	O
several	O
thrusting	O
maneuvers	O
needed	O
to	O
rendezvous	O
with	O
the	O
Soyuz	O
spacecraft	O
was	O
done	O
on	O
the	O
HP-65	B-Device
and	O
compared	O
with	O
the	O
results	O
calculated	O
by	O
the	O
onboard	O
Apollo	B-Application
Guidance	I-Application
Computer	I-Application
.	O
</s>
<s>
Another	O
program	O
for	O
the	O
HP-65	B-Device
allowed	O
the	O
crew	O
to	O
compute	O
pointing	O
angles	O
for	O
the	O
spacecraft	O
antenna	O
for	O
aiming	O
at	O
the	O
ATS-6	O
communications	O
relay	O
satellite	O
.	O
</s>
<s>
In	O
the	O
same	O
year	O
,	O
Mitchell	O
Feigenbaum	O
,	O
using	O
the	O
small	O
HP-65	B-Device
calculator	O
he	O
had	O
been	O
issued	O
at	O
the	O
Los	O
Alamos	O
National	O
Laboratory	O
,	O
discovered	O
that	O
the	O
ratio	O
of	O
the	O
difference	O
between	O
the	O
values	O
at	O
which	O
successive	O
period-doubling	O
bifurcations	O
occur	O
tends	O
to	O
a	O
constant	O
of	O
around	O
6692	O
...	O
</s>
