The Museum of HP Calculators

HP-81

The HP-81 was a top-of-the-line desktop printing calculator which was built like a tank using the same structural foam case as the HP-9805. It used a contactless keyboard with keys that looked and felt like those of a selectric typewriter. The printer used adding machine paper and printed using a red/black ribbon.

To the features of the HP-80, the HP-81 added:

• Logarithm (base 10)
• 20 storage registers (0-9 and .0-.9). (A huge number of registers for its time and the first time the decimal key was used to indicate a second bank of ten registers.)
• Constant arithmetic from register 0 via the *k and /k keys.
• Extended functions via the Ext() key:
  • 0: Interest Per Period
  • 1: Discounted Rate of Return
  • 2: Declining-Balance Depreciation Schedule
  • 3: Diminishing-Balance Depreciation Schedule
  • 4: Sum-of-the-Digits Depreciation Schedule
  • 5: Rule-of-78's Prepayment
  • 6: Amortized Loan Schedule
  • 7: Odd-days Interest
  • 8: Coupon-Equivalent Yield
  • 9: Percent of Total
• User selectable calculating modes selected via the M() key:
  • 0/1: Pre-tax/After Tax
  • 2/3: Annual/Semiannual Coupon
  • 4/5: 30-day Month/Actual-day Month
  • 6/7: 360-day Year/365-day Year
  • 8/9: Bond/Note
• A PRD key to print the 20 registers.
• A PRM key to print the calculating mode settings.
• Optional automatic insertion of the decimal point before the last two digits.

In addition to the built-in printer, an LED display was optional. If you didn't purchase the numeric LED display, you still got a single LED dot that told you that the machine was busy. Unlike the HP-46, the HP-81 had the option of a buffered keyboard. (Probably only offered on the 81, because it could take some time to solve pre-programmed business problems.)

Picture of HP-81(~88K)
As above but smaller (~42K)
Closeup on the keyboard (~114K)

Manual Available

HP-81 features

Dimensions and Weight

Price:

• $925 with printer only
• $1025 with printer and LED display
• $1150 with printer and buffered keyboard but no LED display
• $1250 with printer, buffered keyboard and LED Display

Introduction-Discontinuation: 1973-1975+ (possibly as long as 1978)

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