Retro Review: Texas Instruments TI-68
Company: Texas Instruments
Years: 1989 - 2002
Type: Scientific, Formula Programming
Memory: 440 bytes, in 55 8-bit registers
Operating
System: Algebraic
Memory Registers:
Up to three characters
Batteries: 1 CR2032
Hard to
Find: One with a good screen is hard to
find. It took me two tries to do
so.
Features
The TI-68 is a popular
scientific calculator and back in the day, it had pretty much most of the bells
and whistles (with the obvious exception of graphing):
* Base Conversions and Boolean Logic (9 bits,
signed integer, max binary value: 511, minimum binary value: -511)
* Linear Regression
* Polynomial Solver: Quadratic, Cubic, Quartic
* Simultaneous Equation Solver: Up to 5 x 5 systems
* Expanded Storage Arithmetic: +, -, *, /, ^, Δ%, and, or, xor
* Number Parts:
signum, integer, fraction, real, imaginary, absolute value (but strangely
enough, no argument/angle function, did TI run out of space?)
Complex Numbers
What I love
about the TI-68 is how complex numbers are integrated in the operating
system. There is no need to switch to a
separate mode. Best of all, the TI-68
handles exponential, logarithmic, power, and trigonometric functions with
complex numbers.
The
simultaneous solver also allows for complex numbers. This is indeed rare, as not even most
graphing calculators’ simultaneous solving apps allow for complex numbers as
coefficients. (Note: The HP Prime’s simult
command allows for complex numbers)
Complex numbers
on the TI-68 are notated as such:
Rectangular: (x, y)
Polar: (r ∠
θ)
Part extraction
of complex numbers works slightly different:
real and imag extract the real and imaginary portions of the complex number,
regardless of setting.
Choosing the Precision?
The TI-68
allows for two precision settings: 10 digits
or 13 digits. The display uses 10
digits. I think this is a rarity, if not
a completely unique feature, since calculators in general uses an accuracy of
13 to 15 digits automatically.
I tested a
couple of integrals and the precision setting does not affect the length of
time either way. Both integrals were
calculated in about 3 seconds.
Test Integral
1: ∫ (T^3 * e^(-T) dT, 0, 100, intervals
= 6)
Test Integral
2: ∫ (X^2/(X^2 + X – 1) dX, 25, 75,
intervals = 12)
Integration
The TI-68 uses
the Simpson’s Rule during integration.
To integrate, during evaluation, designate the variable to be integrated
by pressing [CLEAR], [ 3rd ], [ Σ+ ] (dx).
Formula
Programming
The TI-68 has
formula programming. There are no loops
or comparison tests, but all variables are local, meaning their stored values
can be transferred between formulas.
Something I
learned about the TI-68: you can have variables up to 3 characters.
Each formula
can be evaluated (right hand side of the equation) by pressing [SOLVE]. Each variable can accept a real or complex
number.
Keyboard
Let’s talk
about the keyboard. The keys are nice
and responsive. But get a look of all
those shift keys! There are two shift
keys, [ 2nd ], [ 3rd ], along with an inverse key [ INV ]. This is reminiscent of the 1974 Hewlett
Packard HP 65 calculator, where its shift keys were [ f ], [ f^-1 ], and [ g ].
Here is what
the inverse [INV] key (it’s like a “4th” key) operates on:
Key
|
[ INV ] Key
|
Key
|
[ INV ] Key
|
[2nd]
(DRG>)
D: D to R
R: R to G
G: G to D
Angle conversion*
|
D: D to G
R: R to D
G: G to R
|
[2nd]
(>DD)
Convert:
DMS>DD
|
Convert:
DD>DMS
|
[HYP]
Hyperbolic
|
Inverse
hyperbolic
|
[2nd]
(P>R)
Polar to
Rectangular
|
Rectangular
to Polar
|
[SIN] Sine
|
Arcsine
(sin^-1)
|
[2nd] (in-cm)
Inches to
centimeters
|
Centimeters
to inches
|
[COS] Cosine
|
Arccosine
(cos^-1)
|
[2nd] (gal-l)
Gallons to
liters
|
Liters to
gallons
|
[TAN] Tangent
|
Arctangent
(tan^-1)
|
[2nd] (lb-kg)
Pounds to kilograms
|
Kilograms to
pounds
|
[ Σ+ ] add a
data point
|
Erases the
last data point (Σ-)
|
[3rd] (°F-°C) Fahrenheit to Celsius
|
Celsius to
Fahrenheit
|
‘* D = Degrees, R = Radians, G = Grads. Angle mode is unaffected. To change angle mode, press [ 3rd ] (DRG) (it
cycles Degrees, Radians, Grads).
The Basic
Cousin, TI-60X
 |
| TI-60X (left), TI-68 (right). Their memory capacities are shown. |
In 1991, Texas
Instruments released a more basic version of the TI-68, the TI-60X. For more details, check out this link: http://edspi31415.blogspot.com/2017/01/retro-review-ti-60x.html.
Final Verdict
I regret not
getting the TI-68 when it first came out (which would have consisted in asking
my family for one). It’s finally nice to
have one and it’s worth the hype and praise it got.
Eddie
This blog is
property of Edward Shore, 2017
