Retro Review: HP 65

Retro Review: HP 65

Quick Facts

Company: Hewlett Packard

Years: 1974 - 1977

Type: Scientific, RPN (Reverse Polish Notation)

Memory: 9 memory registers, 100 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.

The HP 65 is first programmable calculator. I recently purchased a HP 65 from Persnickity Antiquity in Pomona, California. I saw that HP 65 a year earlier. What got me to purchase was it was for two reasons, (1) I have a HP 67 and fell in love with the classical HP calculators and (2), it had the AAA battery pack (see waterhosko above).Originally the HP 65 is ran with rechargeable Ni-Cad batteries.

Format Settings

The HP 65 has two format settings:

Scientific Format: [ DSP ] # (0-9)

Fixed Format: [ DSP ] [ . ] # (0 – 9)

Modifier Keys

There are three modifier keys: two orange shifts [ f ] and [ f^-1 ] and one blue shift [ g ]. The label for the orange shift is above the key and the label for the blue shift is below the key.

Inverse Key Table

[ f ]	[ f^-1 ]
LN	e^x
LOG	10^x
√x	x²
SIN	SIN^-1
COS	COS^-1
TAN	TAN^-1
R→P (to polar)	P→R (to rectangular)
D.MS+	D.MS-
→D.MS (decimal, minute, seconds)	D.MS→ (decimal)
→OCT (to octal base)	→DEC (to decimal base)
INT (integer part)	FRAC (fractional part)
SF 1/SF 2 (set flag 1 or 2)	CF 1/CF 2 (clear flag 1 or 2)
TF 1/TF 2 (is flag 1 or 2 set?)	TF^-1 1/TF^-1 2 (is flag 1 or 2 clear?)

Programming

Program Steps

In program mode, the HP 65 displays only the key code. The key code is usually two digits, the first is the row (top-down), second is column (left-right). The exception is the digit keys where they would be labeled in the format 0#.

Editing is limited to SST (single step forward) and delete key ([ g ] [ Clx ] (DEL)).

Partially Merged Steps

The first programmable calculator holds up to 100 steps. Steps are partially merged. The program commands that are merged are:

STO # (1 – 8) * does not include storage arithmetic	Swap X and Y: x<>y	Comparisons: x≠y, x=y, x≤y, x>y
RCL # (1 - 8)	Roll Down: R↓	All but STO/RCL are followed by the [ g ] shift key.
NOP (No operation)	Roll Up: R↑

Memory Registers

The HP 65 has nine memory registers R1 through R9. There is no R0 (register zero), which would be added in later calculators.

Two registers are used for specific purposes:

R8: Register 8 is used the counter in the DSZ command (Decrement and Skip if Zero command).

R9: Register 9 is used as a temporary register from trigonometric function calculations, rectangular/polar conversions, and for comparison tests, R9 is used as a Last X register.

R8 and R9 can be used for general use, but would be subject to change.

Comparisons and Labels

The HP 65 has four comparisons (x = y, x ≠ y, x ≤ y, x > y) and the DSZ command operate somewhat like most RPN calculators: if the test is true, the next step is executed. However, if the result is false, the next two steps are skipped. That’s right, the next two steps.

Example:

x > y

[ if true, x > y, execute this step; if false, x ≤ y, skip this step ]

[ also skip this step if x ≤ y ]

[ third step ]

Why two steps? The goto (GTO) command takes two steps on the HP 65. The HP 65 has 15 labels, 0 – 9 and A – E. If both steps are not needed, one can be filled by the NOP (No Op (Operation)) command.

Subroutines and Instant Labels

The labels A through E (A, B, C, D, E) are user programs that can be accessed by keys. They are the only labels act as subroutines. There is no XEQ/GSB command, subroutines are automatically called by pressing the corresponding key. Only one subroutine can be called at a time.

One quirk for the HP 65, if there is a program without a label A, then pressing [ A ] in run mode, execution starts from the first step.

The HP 65 loads five short default programs every time the calculator is turned on, which function is printed above the key in white:

[ A ] 1/x

[ B ] √x

[ C ] y^x

[ D ] R↓

[ E ] x<>y

Non-Continuous Memory

The memory on the HP 65 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 can hold 100 steps.

I love the classic RPN HP calculators from the early 1970s. I have three of them now, the HP 45 (1973), HP 65 (1974), and HP 67 (1976).

Sources

“HP 65” The Museum of HP Calculators (MoHPC). https://www.hpmuseum.org/hp65.htm Retrieved April 1, 2026.

“HP-65 Programming” The Museum of HP Calculators (MoHPC). https://www.hpmuseum.org/prog/hp65prog.htm Retrieved April 1, 2026.

Hewlett-Packard. HP-65 Owner’s Handbook. Cupertino, CA. July 1974.

Eddie

All original content copyright, © 2011-2026. 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.

Retro Review: Casio fx-4000P

Retro Review:   Casio fx-4000P

Quick Facts:

Model:  fx-4000P

Company:  Casio

Years:  1985 - 1989

Battery:  2 x CR2032

Display:  10 digits, 2 digit exponent

Logic:  Algebraic - type in expressions the way you write them

Memory:  Up to 550 programming steps or up to 94 memory registers

Contrast Wheel

Wallet with operation guide (if included, depends on where you buy from)

The Casio fx-4000P holds up its value as it is a popular vintage programming calculator. Prices are about $30 US and above.  

 

Features

Four Basic Modes:

* COMP:  Computer Mode, general calculations

* BASE-n:  Base conversions in the standard four bases decimal, binary, octal, and hexadecimal.  Boolean functions and, or, not, and neg are included.   Binary numbers have a 32 bit capacity, in 4 blocks of 8 each.  

*  SD:  Single Variable statistics

*  LR:  Linear Regression, y = A + Bx

Statistics Variables:

U = Σx^2

V = Σx

W = n

P = Σy^2

Q = Σy

R = Σxy

A = y-intercept

B = slope

r = correlation

As with many Casio calculators, the rectangular and polar conversions store their results in two variables.   For the fx-4000P:

Pol(x,y) stores r in I, Θ in J

Rec(r,Θ) stores x in I, y in J

This is the same as the Casio current fx-5800P.  

The fx-4000P has integer part (Int), fractional part (Frac), and absolute value (Abs).  

Memory and Arrays

The Defm mode allows the user to set the number of memory registers.   The minimum amount of memory registers is 26 (A - Z).   The user can add additional registers at a cost of 8 programming steps each, up to 94 memory registers (leaving only 6 programming steps).   

The fx-4000P allows for indirect storage, which takes the form of:

letter[# of steps from that letter]

For example:

A[0] returns what is stored in A,

A[1] returns what is stored in B,

A[2] returns what is stored in C,

and so on.

By allocating additional registers, 

Z[1] returns what is stored in the 27th register,

Z[2] returns what is stored in the 28th register,

Z[3] returns what is stored in the 29th register,

and so on. 

Variables are allowed.  For example, if 2 is stored in I,  then:

15 → A[ I ] stores 15 in C (2 steps from A).

  

The tilde command is allows us to store a value in multiple registers.  The tilde acts like a Fill function.

For example:  12 → A ~ D  stores 12 in A, B, C, and D.  

Programming

The programming mode of the fx-4000P has a capacity of 550 steps, which can be allocated into 10 slots, Prog 0-9.   The maximum step capacity is reached when the minimum of memory registers is set, 26.  (Defm 0).  The language is Casio Basic:

:

colon that ends each line (except for ◢)

→   

store 

◢  

stop and display (Disp indiciator lights up)

Goto/Lbl #   

up to 10 lables 0-9

Isz var  

increment var by 1 and skip next command if var = 0

Dsz var

decrement var by 1 and skip next command if var = 0

Use Isz and Dsz to simulate For-Next loops

[test]  ⇒ [do if true, skip if false] : [ next command ]

simple If/Then jump structure (displayed on the keyboard is a solid, bold arrow)

Prompting is a little different, as the string must be followed by a colon, then a question mark is used:

"prompt" : ? → var

Example:   Prompt for the user to enter an angle and store it A.   

"ANGLE" : ? → A

We can display a string for a brief pause, simulating a Wait command by this:

"time" → var : Lbl # : "string" : Dsz var : Goto # 

For example, the string "45" is displayed for 25 counts:

25 → I : Lbl 1 : "45" : Dsz I : Goto 1

Strings can also contain the characters engineering symbols k, m, μ, n, p (but not use these in calculations), a solid square, and the angle symbols °, ^r, and ^g (which also allow the user to override the current angle). Strangely, the symbols Θ and % are not included.  

The use of Prog (key is labeled [Prg]) in programs will allow for the use of subroutines.  For subroutines, an implied Return command is added to the end of the subroutine.  

To save space, use → without closing all the parenthesis.  The Ans (last answer) can also be used in between steps.   In COMP mode, pressing equals closes all pending parenthesis.  

The programming structure of the fx-4000P, along with the fx-7000g and fx-6300g,  provide a base for future Casio programming and later graphing calculators.  

Sample Programs:

(spaces and returns provided for readability)

PO:  Σ( (A*x+B)^C from x = 0 to N )

(65 steps)

"A" : ? → A :

"B" : ? → B :

"C" : ? → C :

"N" : ? → N :

0 → S :

Lbl 1 :

S + (A N + B) x^y C → S

Dsz N : Goto 1 : 

S + B x^y C → S

Examples: 

A = 2, B = 6, C = 2, N = 4;  Result = 540

A = 5, B = -2, C = 3, N = 5;  Result = 20727

P1:  Payment of a Mortgage

(64 steps)

P = loan amount

R = periodic rate

N = number of payments

M = payment 

Cash flow convention is followed.

Fix 2 :

"PV" : ? → P :

"RATE" : ? → R :

"N" : ? → N :

.01 R → S :

"PMT" ◢

-P S ÷ (1 - (1 + S) x^y ( -N → M ◢

Norm

Example:

Monthly payment of a $320,000.00 loan at 4% annual for 30 years.

P = 320000, R = 4 ÷ 12, N = 30 × 12; Result -1527.73  (payment of $1,527.73)

If you want to a series of programs for the fx-4000P and possible what they would look like for the fx-5800P/graphing calculators, please let me know in the comments. 

Closing Thoughts

The Casio fx-4000P is a good, entry level programmable calculator which includes a good amount of programming steps.  

The fx-4000P reminds me of the current Casio fx-3650P(II) and what the latter lacks.   I wish the next incarnation of the fx-3650P had the integer, fractional, absolute value, and the ability to use strings with the full alphabet.   The only advantage the fx-3650P has is the derivative, integral, and fractions. 

The fx-4000P runs decently fast and the screen has a big display of characters and results, and it holds up as a favorite.  

Eddie

All original content copyright, © 2011-2022.  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. 

Review: Swiss Micros DM41X

 Review: Swiss Micros DM41X

General Information

Company:  SwissMicros, https://www.swissmicros.com

Type:  Programmable Scientific

Memory:  319 registers (at default) - calculator; 32 MB external flash

Battery:  CR 2032

Date:  September 2020 - current

Cost:  229 CHF, about $257.34 according to currency converter on December 12, 2020 (https://www.xe.com/currencyconverter/convert/?Amount=229&From=CHF&To=USD)

Current Software Version:  2.1 (November 13, 2020)

Case Included?  Yes

The DM41X is a long waited calculator, and joins the DM 41L and DM41 family.  The family runs HP-41CX firmware, including a clock, time, and date functions.    On February 23, 2018, I reviewed the DM 41L which you can see here:

http://edspi31415.blogspot.com/2018/02/review-swissmicros-dm41l.html

I am going to address the features that are specific to the DM41X, which is added to all the great features of the DM41 and DM41L.  

A Return to the Original Layout

The DM41X's keyboard is in a portrait design, like the original Hewlett Packard HP-41C family (HP-41C, HP-41CV, HP-41CX)

Instead of the row of ON, USER, PRGM, and ALPHA keys on the top row, the DM41X adds a column of keys to the right of the main keyboard:

ON/CLK:  ON/OFF button, the shifted CLK displays the current time

USR/SETUP:  The user keyboard.  SETUP shows the DM41X's system menu where stve states and RAW progams can be saved, USB communication can be activated, modules can be saved and loaded, system settings can be changed, and accessing the About screen.

Blue Key:  This is the ALPHA key

Backspace Key

Up Arrow: for program scrolling and debugging

Down Arrow: for program scrolling and debugging

PRG/SIZE:  The PRGM button.  The shifted function allows the user set the number of registers to be set for numerical constants.

R/S/VIEW:  Run/Stop Key, View prompts for a view of a register's value without affecting the stack.

The Big Screen

The DM41X has three screen settings that is set by the DSP key:

1.  All four stacks, T, Z, Y, and X are displayed.  This is my preferred display. 

2.  The X stack and the Alpha Register are displayed.  On the top of the screen:  alarms, the number of storage registers designated for numerical constants, free memory, the current program loaded and it's pointer location.  

3.  Two stacks, Y and X are displayed. On the top of the screen:  alarms, the number of storage registers designated for numerical constants, free memory, the current program loaded and it's pointer location.  

Connectivity

The DM41X's connectivity interface is in line with the DM42's connectivity interface.  Simply plug the DM41X with a USB-Micro B port, then on the calculator press [shift], [USR] (SETUP), 1 for File, 5 for Activate USB Disk.  The DM41X now acts as a USB storage device like a smart phone.  

You can take screenshots by pressing and holding [SHIFT] and [DSP].  Screen shots are saved as .bmp files under the disk's SCREEN folder.

Black and white images of 400 x 240 pixels, 1 bit depth, .bmp format, can be saved to the disk's OFFIMG folder.  Every picture in the folder will be shown on a rotated basis every time the calculator is turned off.  

Custom Menu

Pressing the CST key will give you access to a custom menu 16 available slots for commands and programs.  CST also gives access to Help, ROM Map, and USB Disk activation.  To learn about how to set up the custom menu, click here:  https://edspi31415.blogspot.com/2020/10/swiss-micros-dm41x-custom-menus.html.

Programming

The DM41X operates like the HP-41CX in its programming language except the DM41X has a lot more room for ROM modules.

Verdict

Like the DM41L, the DM41X is a winner.  The keys feel good, I love seeing all four stack levels on the screen, and I am fan of the custom menu built into the DM41X.  This is definitely worth a purchase.

If the price tag of DM41X is too high, consider the DM41 or DM41L.  They may not have a four line display or a custom menu, but the high-quality calculator software and firmware is still present.  Currently only the DM41L is in stock from Swiss Micros, at CHF 129.  

- - - - - -

Announcement

This is the last post for 2020.  I want to wish everyone Merry Christmas, Happy Holidays, and Happy New Year.  2020 has been a brutal year in every respect.  May 2021 be free from disease, war, economic, social, and spiritual struggle; and be full of joy, health, and happiness.  Thank you to my blog's followers and readers; I appreciate all of you!  Take care, and the next schedule blog will be on January 2, 2021.  

Eddie

All original content copyright, © 2011-2020.  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.