Appendix D

Operating Characteristics

Operating Limits

Accuracy of the HP-80 varies according to the operation being performed.
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.
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.
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.
Execution Time
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.
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 1099, 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 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).