**Retro Review: Texas Instruments TI-66**

**Quick Facts**

Company: Texas Instruments

Years in Production: 1982 to 1985

Original Price: I estimate the original price to be from $70 to $100

Battery: 2 x LR44 or 2 x AR76

Type: Scientific, Keystroke Programmable

Operating System: AOS

Number of Digits: 10

Memory: 512 steps, which can be allocated to a maximum of 64 memory registers

Accessories: Carrying Case, PC-200 Printer

I paid $7.99 at a Goodwill in Cerritos, CA. The calculator came with the carrying case, User Guide, and Quick Start Guide, all boxed up. What a lucky find!

**The Next Generation of TI-58C**

The TI-66 was slated to be the next generation of the TI-58C of 1978. Virtually the keyboard design and commands of the TI-58C are present in the TI-66, but there are some differences:

* The TI-66 is an landscape form with a gray keyboard, where as the TI-58C (and the related TI-58 and TI-59 has a black keyboard).

* The TI-66 lacks a card reader.

* The TI-66 also lacked a slot for modules.

* However, the TI-66 runs on coin batteries (AR76 or LR44), which can be found easily. The TI-58C family had rechargeable battery packs, which cannot be easily purchased (few vendors sell them online).

* In learn mode, when a step is registered, the TI-66 displays the key you just pressed with its mnemonic.

**Programming With The TI-66**

Keystroke programming is fairly simple with the TI-66. As I mentioned before, the TI-66 displays a mnemonic when a key stroke is registered (think HP 42S, HP 41C, or HP 32SII). Examples are:

[ x^2 ] displays x↑2

[ π ] displays PI

[ Σ+ ] displays Σ+

[ √x ] displays √x

However, when it comes to programming the TI-66, patience is key! The TI-66 takes on average, 1.5 seconds to register a new keystroke in learn (LRN) mode. This is not for the speedy programmers among us. This is my down point about the calculator, but it is not a deal breaker.

**Other Programming Features**

* User labels A, B, C, D, and E; along A’, B’, C’, D’, and E’. There are five keys dedicated to user labels.

* Local labels have an unusual scheme. They are defined by (almost) any key that is not a numeric key. Therefore, we have labels such as 1/x, sin, and ÷. This is carries over from the 1970s TI programmables (TI-57, TI-58, TI-58C, and TI-59).

* 10 user flags: 0-9.

* Indirect addressing

* Storage arithmetic: SUM (STO+), INV SUM (STO-), Prd (STO*), INV Prd (STO÷)

* Comparisons: compare the value in the display with register t. Store amounts in register t with [ x<> t ]. Example: a [ x<>t ] b [ 2nd ] (x≥t) tests whether b ≥ a).

* An [ OP ] key gives access to additional functions and printing commands.

**A Partial List of OP Commands**

OP 01 – 08 deal with printing, while 09 is not a valid code.

OP 10: sign(x)

OP 11: variance(x), variance(y)

OP 12: slope, intercept (linear regression)

OP 13: correlation (linear regression)

OP 14: x’ (predict x, linear regression)

OP 15: y’ (predict y, linear regression)

OP 2#: increase register R0# (0-9) by 1

OP 3#: decrease register R0# (0-9) by 1

**Keyboard**

Other than registering new programming commands, the keys are immediately responsive. The keys are nice to the touch.

**Verdict**

I would recommend the TI-66, especially if you want a TI-58, TI-58C, or TI-59, but don’t want to deal with 1970s rechargeable batteries, or you are on a budget. It is a very nice, feature rich calculator to have.

Eddie

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