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Appendix D
Operating Characteristics
Operating Limits
Accuracy
Accuracy of the HP-80
varies
according to the operation being per-
formed.
Arithmetic
operations
(+,
-
, X,
-7-)
are
accurate
to 10 digits
±
1
count; that is, the value of the
10th
digit could be
1 less or I more than
the value displayed.
YTM
Special operations
solved
through an iterative method (
•
•
and
•
) *
use numerical analysis techniques formerly requiring com-
puters or large-scale programmable
calculators.
These operations are
accurate to 5 digits.
The
y'
function (which
is
used in the top row financial operations)
produces an answer corresponding to
some x within
±
7 counts in the
tenth least significant digit of the
input
x, and some
y
within
±
4 counts
in the tenth
least
significant digit of the input
y.
Execution Time
Execution time for
iterative
solutions varies according
to
the numbers
you enter. For example,
in
certain
interest
rate calculations the solu-
tion time is related
to
the ratio PV
/
(PMT x n) or FV
/(PMT
x n). Ex-
treme cases outside those normally encountered may require minutes.
Range
Financial calculations using
the
top row of keys are not permitted for
interest rate values very close or equal to 0; specifically, rates between
i=
-0.0000001
% and
i= +
0.0000001
%
are not handled.
Error Indicators
Range
Errors
Any computation or data
entry
resulting in a magnitude greater than or
equal to 10
",
or
less
than 10-
99
,
triggers
an
error signal indicated by a
blinking display.
-Bond yield calculations
may result
in slightly reduced accuracy
if
the
problem is
an
unusual case such as
calculating
a 50% yield-to-maturity for a 2% bond.
For
ex-
ample,
the
yield-to-maturity on a 2% bond,
maturing in
3 years, 3 months and selling
at
26.4B1133 is
50.00%.
The
answer
displayed
is 49.99%.
The
formula for deter-
mining
error
magnitude is,
percent calculation error for bond yield
-s:
2
x
yield
(actual!
x
coupon
x
10-'.
The
operating
limits for the
bond yield algorithm are
defined
such
that
the
price
of the bond must be above 20 and below 5,000, and
coupon must be greater
than
,/,
%
and less than
th
e
price of the bond (expressed as
a
percent
of par).
67
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