There were a wide variety of scientific calculators in our Maths class in 1981. In 2025 I bought a Casio FX-180P to compensate for my original Casio FX-180P that got broken! It's great calculator with lots of features.
Although Casio calculators were the most popular at school at the time, other schoolmates had different makes. In my mind, I recall the TI-30LCD was one of the worst, but was it really that bad?
So, I bought one off eBay too! It turns out it's quite easy to make it says Hello!
Introduction
This was Texas Instruments' first attempt to update their much earlier TI-30 LED scientific calculator, which had been quite popular. They copied the late 70's brushed-aluminium look to make it seem more trendy and Japanese. The sideways view was pretty ugly though, because they tried to make it really thin, but then stuffed it up by adding a bulky 'AA' battery compartment instead of lithium coin cells!
Why? Cheap batteries? To make it incline to compensate for the poor LCD contrast?
It does have one nice touch, the [ON/C] button is slightly recessed: 1mm lower than the others and has a prominent surround to stop users accidentally turning it on when it's bouncing around in a haversack.
The buttons are pretty stiff though, requiring some force before clunking down, which although I think these are a bit worn after 44 years, it's much like I remember when borrowing a school-mate's TI-30 briefly. The layout is quite clever though; adding keys on both sides of the numbers makes for a pleasing symmetry.
On the positive side it can do the basic scientific stuff: π, Trig, logs, factorial and BOOBS! It's only got 8-digits + a dedicated '-', so 99-BOOBS- is its limit! Also interestingly, it displays "Error" in text using the LCD segments whereas Casio calculators just said: "E"
It's slow and inaccurate. 69! takes 1.34s on my FX-180P, but 7s on the TI-30 😮 ! The sin⁻ⁱ(cos⁻ⁱ(tan⁻ⁱ(tan(cos(sin(1)) test says 1.4756033, whereas my FX-180P says: 1.00020289 (it should be 1).
Finally, it lacks a specific stats mode which makes computing standard deviations a real pain and only has 4 levels of brackets (the Casios had 6). OTOH it can convert from degrees to radians if you press a number then [INV] [DRG>].
This calculator travelled 122 miles to get to me, but originally it was bought for a company, just 16 miles from where I live!
Stats
I played around with the calculator for a while and cleaned it up. Then I did a bit of thinking and realised that it is in fact possible to compute statistics fairly easily!
The standard Casio Calculator stats mode could compute all the functions you needed (like population and standard deviation, or averages) from three variables:
- n: the number of items entered.
- ∑x: the sum of the items.
- ∑x²: the sum of the squares of all the items.
In theory this means you need 3 memories. We can reduce it to 2 by simply counting n, the number of items. But the TI-30 only has one memory. Or does it?
The trick is to use the internal memory to compute the sums, and the calculator stack to compute the ∑x² terms. And this is possible, because as well as a [STO] and [RCL] button on the calculator, it also has a [SUM] button.
So, we can use [SUM] to store the ∑x terms as you enter each one and [x²] [+] to compute the running ∑x² total.
For example, let's say we have the data: {5, 4, 8, 3, 4, 5, 7, 4, 3}.
First, you'd press: [0] [STO] to clear memory and the display.
Then
| Number |
∑x Term |
Generate x² (Display) |
∑ (Display) |
| 5 |
[SUM] |
[x²] 25 |
[+] 25 |
| 4 |
[SUM] |
[x²] 16 |
[+] 41 |
| 8 |
[SUM] |
[x²] 64 |
[+] 105 |
| 3 |
[SUM] |
[x²] 9 |
[+] 114 |
| 4 |
[SUM] |
[x²] 16 |
[+] 130 |
| 5 |
[SUM] |
[x²] 25 |
[+] 155 |
| 7 |
[SUM] |
[x²] 49 |
[+] 204 |
| 4 |
[SUM] |
[x²] 16 |
[+] 220 |
| 3 |
[SUM] |
[x²] 9 |
[+] 229 |
At this point the calculator shows 229 (∑x²). Pressing [RCL] gives you 43 (∑x) and manually you count n=9.
So, then:
- Average=[RCL]/9=4.78;
- Standard Deviation=√(∑x²/n -(∑x/n)²= √(229/9-(43/9)²)= 1.62.
It's better to clear the memory first and then use [SUM] all the time even though you could do 5 [STO] for the first one, because it allows you to repeat the pattern and avoid thinking.
I don't think this was actually taught as a technique at school. Instead they expected you to compute ∑x terms, then go back and compute the ∑x² in a new column, before summing each column and then calculating the variance (rather than the Standard Deviation). This technique avoids entering the numbers twice. It's still somewhat slower than using a Casio with its Sd mode, but at least it's quicker than a purely manual mode.
Correcting Errors
I've also worked out how to correct data entries too. Let's say you mis-entered 5307 as 5607 by typing:
5607 [SUM] [x²] [+]
On an FX-82 you'd just do 5607 [DEL] and it would correct it. But on a TI-30 there's no such button (just as there isn't an [x] button). But correcting data is almost as easy. You type:
[-] 5607 [+/-] [SUM] [X²] [+]
On a real TI-30 LCD you're much more likely to miss or double-type a digit due to the dodgy debounce (it shares LCD and keypad pins so it can't display and read keys at the same time), so correcting errors is important.
The TI-30 isn't RPN, so the [+] at the end of each line signifies that the next calculation will be another addition, but also gives you the running total. So, the initial [-] overrides the previous [+] so that when the [+] is hit at the end, it subtracts 5607². But when you enter the number, you can't type [SUM] to delete the ∑x term, because the number on the display will be positive. You need to hit [+/-] to make it properly negative and then hit [SUM]. When you hit [X²] it makes it positive again so the earlier [-] will subtract, as you intend. Also, it wouldn't work to type in 5607 [+/-], because when you later hit [X²] it'll become positive again.
Conclusion
The TI-LCD was already a poor calculator by the standards of the early 1980s. It lacked functions other calculators had as standard and accuracy was poor. However, a critical statistical mode can be implemented fairly easily, and can roughly halve the number of keypresses to compute.
