Hewlett Packard HP-55

Serial Number 1509S09173: 1975, 9th week, Singapore
Accessories Pouch

Power supply

Manual: HP-55 Owner's Handbook (Bound printout from the MoHPC CD-ROMs, 2/1975)

Quick Reference: HP-55 Kurzanleitung (Bound printout from scanned PDF, German, 33 pages, 12/1974)
Condition Absolutely excellent! Even the battery pack still works and there's no corrosion inside. There is no back label but there are no glue stains so maybe there has never been one.
Acquired 9.9.2002
HP codename, series Merlin, Classic
Type, Precision, Input Mode Scientific, 10 BCD digits, exponent 99, Reverse Polish Notation
Programmable Unmerged instructions, no editing, no subroutines, no symbolic labels.
Performance Index 1.0. One of the slowest computers in my collection.
Memory 20 registers, 49 program steps
Display 13 digit 7 segment red LED plus sign
Special features Built-in accurate quartz timer, linear regression, many conversions. The timer software was present in the HP-45 as well but wasn't officially supported due to the lack of an accurate crystal. Once in timer mode (enabled by a switch below the display), the following commands are available:
  • R/S toggles timer between running and stopped.
  • CLx resets the timer to zero both in stopped and running mode.
  • EEX turnes on/off the 1/100th second display.
  • 1 - 9 stores the current time in the corresponding register when the timer was running or recalles the stored time when the timer was stopped. 
Original Pricing, Production 1.1.1975 ($395) - 3.1.1977 ($335)
DM 1150 in 1976 (according to Kurt Pribil).
Batteries 3x AA pack or AC power supply
Dimensions Length 15.1cm, Width 8cm, Height 3.6cm
Links HP-55 Owner's Handbook (PDF, English, 108 pages, 2/1975)
HP-55 Kurzanleitung (PDF, German, 33 pages, 12/1974)
Quick Reference (PDF)
Comment HP's sixth calculator and the second programmable after the HP-65. It's outstanding feature is the built-in timer with its support for up to 10 split time measurements. Other than that pretty straight forward with a quite poor programming model similar to the HP-25C
Registers used for summation and linear regression:
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