Retro Review: TI-68

[Eddie W. Shore]

Excerpt:

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

Link: http://edspi31415.blogspot.com/2017/07/r...ti-68.html



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)

[ijabbott]

Yes, I don't know who in their right mind at TI thought it was a good idea for the 'real' and 'imag' functions to operate like that! Almost as bad as the TI-84's exponential format showing angles in degrees.

[jhallen]

I remember these, thought they were pretty good looking calculators when they came out. I think the Radio Shack version of it looks even better.

But I find the user interface to be somewhat inefficient- I wondered if they were trying to avoid looking too much like Casio fx-4000p:

There is no backspace, only delete (and it's shifted).

When you hit Shift-ANS, it puts the actual number in the edit buffer, not symbolic "ANS". RCL does the same thing. You could make arguments either way for this.

You have to hit Alpha after RCL, even though the variable must be a letter.. why doesn't it auto-Alpha?

You can "replay" the previous equation, but it's weird (as a Casio user) that you have to hit Shift-EQN to get it back instead of left arrow.. but whatever.

I like the formula memory, though there are too many prompts when using it. Like do you really want to calculate this formula YN?

Oh one more thing: is this possibly the first calculator with a hard slide-on cover? Maybe first scientific calculator like this..

[Benjer]

(08-08-2021 03:11 PM)jhallen Wrote:  Oh one more thing: is this possibly the first calculator with a hard slide-on cover? Maybe first scientific calculator like this..

I think that's a really interesting question.

I can't speak with authority but I believe the TI-30 SLR+ predates the TI-68. It has a slide-on cover. I'm betting there are even earlier examples. I thought maybe the fx-7700g but that came out after the TI-68.

The TI-68 is one of my favorite calculators in terms of form and function. It was no longer in vogue by the time I was old enough to have need of a scientific. As Eddie alludes to, the displays seem to be delicate and of the three examples I've laid hands on, all three had issues. I was able to restore one of them to full function using a heat gun on the LCD ribbon connector. It's anyone's guess how long that repair will last.

[jhallen]

My latest acquisition is a fully working TI-68. I already had a TI-68, but with the usual ribbon cable / LCD problems (someone needs to find a fix for this).

Anyway, this is a great complex number formula (non-programmable) calculator. Nearly all functions accept complex arguments. The one disappointment is that factorial is whole number only.

So e^(0, pi) gives (-1, -2.2*10^-13), almost :-)

Its SIMUL function can solve systems of linear equations with complex coefficients, really nice for impedance calculations.

Its POLY function finds all complex roots of up to fourth order polynomials.

It has numeric integration, but it does not seem to have a numeric root finder. It has a "SOLVE" button, but this should be called evaluate- you use it to evaluate formulas.

I think the user interface is kind of weird. There is a key to choose the output mode, rectangular or polar. But it does not convert the current number. There is another key for that, P->R. In polar mode, it reduces any number you enter to -180 to 180 or -pi to pi.

There is a separate key for 2's complement (for binary/hex/octal modes), but as far as I can tell it is completely identical to negate (-), so redundant.

It has real and imag keys- they extract the first or second part of the complex number argument. So if the argument has a complex number in polar form, imag returns the angle.

It has the percent change key- I thought only HP calculators had this.

[Dave Britten]

I have one of these, and it's a pretty neat calculator, though I agree that the user interface is kind of clumsy, particularly with the handling of selection lists and menus and whatnot. In most cases, you're probably better off getting a TI-85 unless you really need that percent-change key.

[jhallen]

Ah, I didn't realize that TI-85 and TI-86 were so different from the TI-84 series. I will give them a try.

[Dave Britten]

(10-24-2022 01:08 PM)jhallen Wrote:  Ah, I didn't realize that TI-85 and TI-86 were so different from the TI-84 series. I will give them a try.

Very different! The 85 and 86 are my two favorite TIs. I've got like 3 or 4 of each.

[carey]

(10-24-2022 07:25 PM)Dave Britten Wrote:  Very different! The 85 and 86 are my two favorite TIs. I've got like 3 or 4 of each.

I like the 86 a lot too but haven't used the 85. As you've used both, I'm curious if there are any advantages of the 85 over the 86, i.e., were any features lost in the more memory and better display 86 model? Thanks!

[Dave Britten]

(10-26-2022 05:42 AM)carey Wrote:  

(10-24-2022 07:25 PM)Dave Britten Wrote:  Very different! The 85 and 86 are my two favorite TIs. I've got like 3 or 4 of each.

I like the 86 a lot too but haven't used the 85. As you've used both, I'm curious if there are any advantages of the 85 over the 86, i.e., were any features lost in the more memory and better display 86 model? Thanks!

Yes, actually. The 85 is about twice as fast as the 86. The elaborate bank switching scheme they had to add to support the huge memory of the 86 caused a major performance hit. Also, the stat/list editor on the 85 is a bit nicer to work with, as it uses a full-size font, and you can quickly jump to the bottom of a list (e.g. to add a new item) by scrolling up while you have the first item selected. And I like the feel of the rectangular 85 keys a little bit more than the rounded keys of the 86.

Of course, the 86 has a better screen, lots more memory, and quite a bit more functions. You can add programs/variables to the Custom menu (not just built-in commands), the OS officially supports running assembly programs, and TI released finance and inferential statistics add-ins that provide functions akin to the 83 Plus, so there isn't a clear argument for either one being strictly better than the other.

[carey]

Thanks Dave for the detailed and helpful answer!