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Appendix D
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Operating Characteristics
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Operating Limits
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Accuracy
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Accuracy of the HP-80 varies according to the operation being performed.
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 Arithmetic operations (+, –, ×, ÷) 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.
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Special operations solved through an iterative method ( i (YTM) and i)
use numerical analysis techniques formerly requiring computers or
large-scale programmable calculators. These operations are accurate to 5
digits.
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The yx 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.
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Execution Time
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Execution time for iterative solutions varies according to the numbers
you enter. For example, in certain interest rate calculations the
solution time is related to the ratio PV/(PMT × n) or FV/(PMT × n). Extreme cases outside those normally encountered may require minutes.
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Range
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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.
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Error Indicators
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Range Errors
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Any computation or data entry resulting in a magnitude greater than or equal to 1099, or less than 10–99, triggers an error signal indicated by a blinking display.
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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 example, the yield-to-maturity on a 2% bond, maturing
in 3 years, 3 months and selling at 26.481133 is 50.00%. The answer
displayed is 49.99%. The formula for determining error magnitude is,
percent calculation error for bond yield ≤ 2 × yield (actual) × coupon ×
10–4. 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 1/8% and less than the price of the bond (expressed as a percent of par).
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