<s>
The	O
HP-55	B-Device
was	O
a	O
programmable	B-Application
handheld	O
calculator	O
;	O
a	O
lower-cost	O
alternative	O
to	O
the	O
HP-65	B-Device
.	O
</s>
<s>
Its	O
outward	O
appearance	O
was	O
similar	O
to	O
the	O
HP-65	B-Device
,	O
but	O
its	O
silver	O
band	O
went	O
through	O
between	O
the	O
display	O
and	O
the	O
keyboard	O
like	O
HP-45	B-Device
,	O
its	O
some	O
key	O
functions	O
were	O
different	O
from	O
HP-65	B-Device
and	O
it	O
did	O
not	O
have	O
a	O
magnetic	O
card	O
reader/writer	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-55	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>
Another	O
feature	O
of	O
the	O
HP-55	B-Device
was	O
that	O
it	O
officially	O
featured	O
a	O
stop-watch	O
function	O
much	O
similar	O
to	O
the	O
hidden	O
stop-watch	O
function	O
of	O
the	O
earlier	O
HP-45	B-Device
calculator	O
.	O
</s>
<s>
The	O
data	O
format	O
used	O
by	O
the	O
stop-watch	O
consisted	O
of	O
a	O
combination	O
of	O
units	O
(	O
Hours	O
,	O
Minutes	O
and	O
Seconds	O
)	O
,	O
but	O
the	O
HP-55	B-Device
featured	O
a	O
special	O
conversion	O
function	O
to	O
convert	O
between	O
this	O
format	O
and	O
a	O
pure	O
unit	O
(	O
Hours	O
)	O
.	O
</s>
<s>
The	O
HP-55	B-Device
also	O
featured	O
several	O
other	O
conversion	O
functions	O
to	O
instantly	O
convert	O
data	O
between	O
the	O
Imperial	O
and	O
Metric	O
systems	O
.	O
</s>
