Retro Review: HP 67
I won a HP 67 from the HHC 2025 Conference in Orlando, Florida last September. Be on the lookout for a list of videos by the hpcalc.org's YouTube page soon. It's always a good time.
Bruce Gordon donated the HP 67 to the conference and I'm grateful and appreciative. I love the box, the calculator, the leather cover, and the manuals.
Quick Facts
Company: Hewlett Packard
Years: 1976 - 1984
Type: Scientific, RPN (Reverse Polish Notation)
Memory: 20 memory registers, 224 steps
Batteries: originally Ni-Cad, there are battery packs that can use AAA batteries (Ebay seller: waterhosko, https://www.ebay.com/usr/waterhosko)
DISCLAIMER: I am not page for referring the website on eBay, nor I do not guarantee that inventory is available.
Features:
* Trigonometric, logarithmic, exponential functions
* Probability: n! (the factorial function only accepts positive integers)
* Integer part, fractional part, absolute value, round to fix settings
* Polar/Rectangular, Degree/Radian, Hours/Hours-Minutes-Seconds (HMS) conversions
* Percent and percent change
Non-Continuous Memory
The memory on the HP 67 is not continuous. When the calculator is turned off, all memory is lost. The only way to save the memory registers and the steps require the use of thin memory cards and the built-in card reader. Each card has two sides, which can hold 112 steps per side. With decades-old calculators like the HP 67, the card reader has stopped working. It can be repaired and when I get the chance, I will leave it to the repair experts.
Memory Registers
There are 20 memory registers but they are split up: 10 primary registers and 10 secondary registers. The set of registers can be switch by pressing [ f ] (P<>S). This really comes into play when working with statistical data (see next section).
Statistics
The HP 67 has the standard statistics functions including sums, means, and standard deviations. When calculating statistics, the following stored on the secondary registers:
RS9 (19): n
RS8 (18): Σxy
RS7 (17): Σy^2
RS6 (16): Σy
RS5 (15): Σx^2
RS4 (14): Σx
Clearing these registers require this key sequence: [ f ] (CL REG) [ f ] (P<>S). To access the statistics registers after entering the data, start by pressing [ f ] (P<>S).
The mean function, [ f ] (x-bar):
Y: average of y-values
X: average of x-values
The standard sample deviation, [ g ] (s):
Y: sample deviation of y-values
X: sample deviation of x-values
Programming
As mentioned before, the HP 67 can hold programs up to 224 program steps. Steps involving shift keys [ f ], [ g ], and [ h ], along with [ GTO ] and [ LBL ], are merged with the next key press to help save space. However, each press of the digit keys and the decimal point take one step each. For instance, 475.2 takes five steps ([ 4 ], [ 7 ], [ 5 ], [ . ], [ 2 ]) while sequences such as [ GTO ] [ 1 ] and [ f ] (√x) take one step each.
Always available are five user keys that double as ten lettered labels: A, B, C, D, E, a, b, c, d, and e. The lower case labels are shifted of their capital letter counter parts. There are also ten numerical labels, 0-9, available for use.
There are eight comparison tests:
Gold tests (use the [ f ] shift): x=0, x≠0, x<0, x>0
Blue tests (use the [ g ] shift): x=y, x≠0, x≤y, x>y
The registers I and (i) are used for indirect addressing. We have special functions to store to Register I, the ST I and RC I functions. The DSZ and ISZ only work on register 1.
DSZ: Decrease register I by 1 and skip the next instruction if the result is I=0.
ISZ: Increase register I by 1 and skip the next instruction if the result is I=0.
There are four flags. Flags 0, 1, and 2 are user flags. Flag 2 gets cleared automatically when tested. Flag 3 is the entry flag, which is set automatically when a number is entered or a data card is read. Like Flag 2, Flag 3 is cleared automatically when tested.
For more details, here is an excellent article on HP-67 (and the similar HP-97) programming by the MoHPC (Museum of HP Calculators) web page: https://www.hpmuseum.org/prog/hp67prog.htm
As mentioned before, when the calculator is turned off, all memory is reset. When available, save your programs to a data card first.
Program Collection
Download here:
https://drive.google.com/file/d/114H4D0hcOjxDj_MHQNvwDBUJV3chlpdC/view?usp=sharing
List of Programs (all programs on the file are relatively short, less than 35 steps):
Countdown of HP 67 "seconds"
Random Numbers
Snell's Law
Circle: Area and Circumference
Sphere: Surface Area and Volume
Angle Between 2 Lines with Slopes x and y
Sum of Powers
Adding Complex Numbers
Multiplying Complex Numbers
Complex Number to a Real Power
Permutation
Combination (with duplicating X and Y stack values)
Speed of Sound Approximation (in meters per second)
Finance: Present Value Annuity Factor (including setting N and I% with monthly payments)
Distance Between Two Points (x,y) and (z,t)
Horizontal Curve
When the HP 67 is Turned Off
* All memory is cleared
* The display setting is reset to FIX, DSP 2 (display 2 digits)
* The angle setting is reset to Degrees
Notes
* The number format and the number of decimal points displayed are set separately. For format, the HP 67 offers fixed (FIX), scientific notation (SCI), and engineering format (ENG). For this calculator, do not enter a number after FIX, SCI, or ENG. Setting the number of digits require the use of the display (DSP) key. For instance, if I want to set the HP 67 to fixed setting with 4 decimal places, the keystroke sequence required would be [ f ] (FIX) [DSP] [ 4 ].
* It takes getting used to use a shift key [ h ] before swap (x<>y) and roll down (R↓). Usually they are primary key functions.
* The card reader did not operate, but for machines that are now 50 years old, it's understandable because they do break down. If I get it repaired, I'm leaving it to the professionals.
* There are no internal guard digits. The HP 67, as it seems to be the case for the entire Classic series and possibly later series such as the Voyagers, carries out calculations to fit the 10 digit screen and that's it.
Example:
Set FIX, DSP 9.
2 √ 1.41 - 100 ×
Result:
HP 67 (DSP 9): 0.421356200
HP 45 (FIX 9): 0.421356200
HP 15C CE (FIX 9): 0.421356200
HP 42S, original (ALL): 0.421356237
* This is the only calculator I know that stores the six statistical sum results in secondary registers. I'll have to remember to do the P<>S command first. In later models the registers are not split in this fashion, and that I am grateful for.
* The display is nice, clean, and I do get a small thrill from working with red LED displays.
* There is also a learning curve when all of the shifted functions are listed BELOW the primary keys:
[ primary function ]
h (black)
g (gold) b (blue)
It's a classic for a reason and I love it. The keyboard is clean and the keys are responsive.
Eddie
All original content copyright, © 2011-2025. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.
