Spotlight: AccuMath 400B Slide Rule

Spotlight: AccuMath 400B Slide Rule

Introduction

I purchased an AccuMath 400B slide rule at Antique Station, an antique store in Oro Grande just north of Victorville, CA.

I am impressed of the larger markings on the slide rule. The slide rule very easy to read, yet has a lot of scales for calculations including powers, roots, trigonometry, and logarithms.

The Scales

The slide rules have the following scales:

Top Frame (stationary):

S: Sine of angles in degrees. A = sin(S°) ÷ 100, S° = arcsin(A × 100)

K: Cube and cube root scale associated with scale D. K = D³, D = ³√K

A: Square and square root scale associated with scale D. A = D², D = √A

Slide:

B: Square and square root scale. Scale is from 1 to 100 and it is the same scale as Scale A.

CI: Reciprocal of scale C.

C: Multiplication and division scale from 1 to 10. Same as scale D.

Bottom Frame (stationary):

D: Multiplication and division scale from 1 to 10.

L: Logarithmic and exponential scale associated with D. L = log D, D = 10^L. (base 10 logs)

T: Tangent of angles in degrees. D = tan(T°) ÷ 10, T° = arctan(D × 10)

Note: A lot of slide rules associate the S scale with the C/D scales, but for this particular design, the A scale is used instead.

The Back Side

U.S./Metric Conversions, Equivalents, and Settings (i.e. 1 in mercury = 1.133 ft water)

Fractions up to 64ths and their decimal equivalents (i.e. 47/64 = 0.734375)

Trigonometric Identities, Right Triangles, Law of Sines and Cosines

Example Calculations

Keep your exponents in mind! N = mantissa * 10^exponent

Hairline: the plastic cursor you move around, Slide: the center piece of the slide rule you move around

4 × 2 = 8

Slide C right to match C: 1, D: 4

Move cursor right to C = 2

Read down to D: 8

3 × 9 = 27

Rearrange to 9 × 3. Slide C left to match C:1, D: 9

Move cursor left to C = 3

Read down to D: 2.7

Multiply by 10 since we slide C left: 2.7 × 10 = 27

12 × 33 = 396 (Approximate method)

Rearrange to 33 × 12. Slide B left to match: B: 1, A: 33

Move cursor left to B = 12

Read on A: the cursor is very close to 4.

Multiply by 100 since we moved B left. Result: approx 400.

54 ÷ 9 = 6

Move Slide B to match: A = 54, B = 9

Move cursor left to B = 1

Read A = 6

√81 = 9, 9^3 = 729 (approximate)

On A, slide cursor to 81.

Read on D: 9 (square root)

Read on K: in between 720 and 730. (so ≈725?)

Note that the scales are limited.

√144 = 12 (√(144 ÷ 100 × 100) = √1.44 × √100 = √1.44 × 10)

On A, slide cursor to 1.44.

Read on D: 1.2

Multiply by 10. Result: 12.

Logarithms: D and L scales. L = log D, D = 10^L

log 3 ≈ 0.47712

On D, slide cursor to 3.

Read on L: about 0.47

10^0.55 ≈ 3.54814

On L, slide cursor to 0.55

Read on D: about 3.54

Tangent of Angles in degrees: D and T scales. D = tan(T°) ÷ 10, T° = arctan(10 × D)

Tan(25°) ≈ 0.46631 (approximate)

On T, slide cursor to 25.

Read on D: about 4.65. Divide by 10 for a result of approximately 0.465

arctan(0.7) ≈ 34.99202 (approximate)

On D, slide to 7 (0.7 × 10)

Read on T: close to 35. Result: approximately 35°

Sine of Angles in degrees: A and S scales (for this model!) A = sin(S°)÷100, S° = arcsin(A×100)

sin(30°) = 0.5

On S, slide cursor to 30.

Read on A: 50. Divide by 100 for a final answer of 0.5

arcsin(0.2) ≈ 11.53700°

On A, slide to 20. (0.2 × 100)

Read on S: slightly after 11.5, for an approximation of 11.5°.

Reciprocal: CI and D scales. When the slide is at its home position, that is C = 1 and D = 1 are aligned:

1/CI = D

Find 1 / 4 = 0.25

Slide D to 4.

Read CI at 2.5 and divide by 10. Result: 0.25

Source

Instruction Manual for the AccuMath 400B.

Page 1: https://www.sliderule.ca/stermf.jpg

Page 2: https://www.sliderule.ca/stermb.jpg

Eric’s Slide Rule Page, last updated December 1, 2002. Accessed June 27, 2026.

Best,

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.

The New TI-84 Evo

The New TI-84 Evo

Some Notes on the TI-84 Evo

The TI-84 Evo was released on April 28, 2026 in the United States. It is an update of the TI-84 CE Python and in fact, replacing the TI-84 CE Python. As of right now, the TI graphing calculator the TI-83/84 family consists of:

TI-83 Plus: This calculator model was first introduced in 1999 and is run by four AAA batteries with a CR1620 backup.

TI-84 Plus: This is the base TI-84 model with a monochrome screen, originally first arrived in 2004. The last firmware, 2.55, adds math print (textbook print).

TI-84 Plus CE: This is a color version of the TI-84 Plus and has a rechargeable battery.

TI-84 Evo: This is next version of a TI-84 Plus that has Python.

Quick Facts and What the TI-84 Evo Can Do

Model: TI-84 Evo

Company: Texas Instruments

Type: Graphing

Programming Language: TI-Basic, Python

Power: Rechargeable Battery, powered by as USB C cord

Case: Slide case

Memory: 7 memory registers: A, B, C, D, X, Y, M (M has memory addition and subtraction)

Years in Production: April 28, 2026 - present

Display: 320 x 240 pixels, 2.8” diagonal screen

Colors: White, Pink, Mint Green, Raspberry, Silver, Teal, Lavender. I have a white one.

Retail Price: $160 (US dollars). There is a four year license to an online emulator included.

For reference, the TI-84 Plus CE Python, the calculator the TI-84 Evo replaces, was in production from July 27, 2021 to April 27, 2026.

At this point we all know, more or less, the main features of the TI-84 Plus, as they are present with the current TI-84 Evo (not an all inclusive list):

* Graph up to 10 functions, six parametric functions, six polar functions, and three recursive functions

* Lists can have up to 999 elements can be used. Lists can have real and complex numbers. There are many functions associated with lists, such as sorting, finding the arithmetic average (mean), the sum of the elements, applying lists in statistical analysis, and generating lists from defining a sequence. There are six lists that can be accessed from the keyboard and additional lists with custom names can be created.

* Complex numbers including arithmetic, conjugate, conversion between rectangular (a+bi) and polar forms (re^(iΘ)), square, square root, cube, and cube root of complex numbers.

* 10 matrices, [ A ] through [ J ], including the transpose, inverse, determinant, row operations, and generating identity matrices.

* Many statistical regressions, distributions (normal, student, Chi-squared, F, binomial, Poisson), and ANOVA.

* Drawing tools

* Two programming languages: the classic TI-Basic and Python. Python modules include math, random, plotlib (TI version), time, specialized modules for the TI hub, TI rover, and import processing.

Two major selling points of the TI-84 Evo are:

* Distraction free mathematics with no smartphone interface. However, all calculators that are not downloaded to smartphones qualify to be “distraction free”. This is a response to curbing smartphone use in the classroom.

* The TI-84 Evo has an icon menu. The icon main menu replaces the app key. While the TI-84 Evo is on, the [ on ] key acts as toggle between the main menu and the last used app.

The apps included with the TI-84 Evo are:

1. Calculator (Home)

2. Y= Function Editor (same as pressing [Y=]

3. List Editor (same as pressing [ stat ], [ 1 ])

4. Mode Settings (same as pressing [ mode ])

5. Numeric Solver (same as pressing [math], C or [math], [ ↑ ], [ enter ])

6. Polynomial Root Finder

7. System Solver (linear systems)

8. Finance (time value of money solver and basic finance functions, including date functions covering years from 1980 to 2079).

9. Transformation Graphing

Inequality Graphing

Conics Graphing

Python

TI-Basic

Help (one page has a QR code for which leads to the TI-84 Evo online guide)

TI-84 Evo User Guide: https://education.ti.com/en/product-resources/eguides/eguide-84-evo

Some Differences Between the TI-84 Evo and the Previous TI-84 Plus CE Python

For this section, I refer the TI-84 Plus CE Python as the 84 Python and the TI-84 Evo as the 84 Evo. These are some of the changes observed. Despite these changes, at its core the TI-84 Evo is easy to pick up and learn, and if you are transferring from an older TI-82/83/84, the learning curve is at the most, minimal.

Keyboard Changes:

84 Python: smaller keys, 2nd and alpha functions printed above the keys 

84 Evo: big square keys, 2nd and alpha functions printed on the keys

84 Python  (TI-84 CE Python) Keyboard

84 Evo  (TI-84 Evo) Keyboard

From the 84 Python to the 84 Evo:

2nd of [del] key: ins becomes an icon | <> []

distr (distributions): moves from 2nd of [vars] to alpha of [stat]

[apps] key replaced with fraction template [ []/[] ]

2nd of [math] key: test becomes an icon =≤≠>

matrix: moves from 2nd of [x^-1] key to 2nd of [vars] key

[clear] key gets an undo clear 2nd function, labeled ⟲clear, can be used as "cut"/"copy" and "paste"

[x^-1] reciprocal key becomes [x^[]] power key template, while its 2nd function is the root template []√

Arithmetic keys move up a row: 

[ ^ ] becomes the [ ÷ ] key 

[ ÷ ] becomes the [ × ] key 

[ × ] becomes the [ - ] key 

[ - ] becomes the [ + ] key 

[ + ] becomes the [ <> ] key (utility/toggle key) Though the primary functions change the 2nd and alpha functions remain the same

[enter] key appears to lose the solve alpha function

2nd of [sto→] key: rcl gets lengthened to recall

[on] key gets a home icon

Battery:

84 Python: Lithium ion polymer 

84 Evo: Lithium ion

Power Connection:

84 Python: TI-specific cord with USB-A/USB-mini 

84 Evo: USB-C/USB-A (came in the box)

Colors of the keys – on the white keyboard:

84 Python: blue 2nd key, green alpha key, black math keys, gray arithmetic keys, white number keys, gray function and arrow keys

84 Evo: blue 2nd key, green alpha key, white math, arithmetic, and function keys, black arrow and number keys

number keys: [ 0 ] through [ 9 ], [ . ], [(-)]

Connection Software:

84 Python: TI Connect CE

84 Evo: https://connectevo.ti.com/ticevo/en/ (online connection, like TI-nSpire CX II)

Multiplication Symbol Used in Expressions:

84 Python: asterisk (*)

84 Evo: dot (⋅)

Colors Used on Calculations on the Home/Calculator Screen:

84 Python: Everything is in black

84 Evo: Input expressions are in black, cursor is blue, answers are in green

Memory Available for Storage:

84 Python: 3 MB

84 Evo: 3.5 MB

Graphing Display Area:

84 Python: 264 x 165 pixels with a border around the graphing

84 Evo: 319 x 209 with no boarder as the graph takes the entire screen (just like the old days, the monochrome TI-84)

Backwards Capability of TI-83 Plus and TI-84 Plus TI-Basic Programs:

84 Python: Yes (.8xp)

84 Evo: No (.8xp2). Why? Texas Instruments rewrote the Basic language engine. There are programs that can translate from .8xp to .8xp2 files. Check Cemetech or TI Planet.

Note: Python programs can be transferred easily between the 84 Python and 84 Evo.

Built in Clock:

Python: Set clock option present

Evo: No clock option present (quiet removal, will the clock be missed?)

Features Added to the TI-84 Evo

* Gradian mode, with all the conversions and symbols added

* Three additional regressions: PropReg (y = a*x), RecipReg (y = a/x + b), and eBaseReg regression (y = a * e^(b*x))

* The Time Module adds two additional functions: ticks_ms and ticks_diff.

Should I Get a TI-84 Evo or TI-84 CE Python?

Reasons to buy the TI-84 Evo:

You like connecting with USB C instead of USB Mini

Faster processor*

Your first TI-84 ever

You desire to work with both hardware and the emulator (you get a four year license on purchase)

You want the latest model and/or if you are like me and like to collect calculators

Reasons to buy the now older TI-84 CE Python:

The border around the graphing screen isn't annoying, don’t mind it as much (or at all)

You work with the SciTools and Periodic Table apps a lot

You want a TI-84 with Python at a lower price

You work with the Turtle Module in Python

* although some say graphing could be slower due to the fact the entire screen is used.

Note: If you want assembly programming with a TI, stick with the older monochrome calculators as the newer TI calculators no longer support assembly programs.

Source

Texas Instruments. “TI-84 Evo Graphing Calculator” https://education.ti.com/en/products/calculators/graphing-calculators/ti-84-evo Retrieved May 23, 2026.

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: 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.