For all practical intents and purposes, the TI-67 looks like a much needed upgrade of the popular TI-68 calculator. Not only does the TI-67 have more than three times the memory of its "bigger" cousin, it also offers capabilities that turn the machine into a true programmable: the ability to call subprograms, evaluate expressions conditionally, and execute loops.

Appearance-wise, the TI-67 belongs to the "Galaxy" series of calculators that includes the TI-65 and the TI-66. The TI-67 does, however, have a more robust appearance; it also sports a hard cover that prevents premature battery drain or other malfunctions due to erratic keystrokes that can occur during storage.

The programming model of the TI-67 is essentially a formula programming model, but it does offer advanced features that go beyond evaluating simple expressions. A formula can contain multiple expressions separated by the colon character. Additionally, formula storage is also used to store "programs", that are really formulae that do not readily evaluate to a value; they may contain instead instructions such as goto or lbl that permit complex flow control.

This is best demonstrated by my favorite programming example, the Gamma function. The implementation shown here computes this function's logarithm using the modified Stirling formulae, made accurate for small values with an added iteration. In addition to positive arguments, the formula also evalutes for negative values whose integer part is odd (e.g., -3.5). The program does not prompt for input; it uses instead the result of the last computation (Ans) as its input argument. The program's result is both displayed and stored in Ans for further chain calculations.

LNG:
ans->X:
1->LNG:
lbl L:
if X>9:
goto G:
X*LNG->LNG:
X+1->X:
goto L:
lbl G:
X*ln X-X-ln LNG+ln √(2*π÷X)+((((1÷1188÷X2-1÷1680)÷X2+1÷1260)÷X2-1÷360)÷X2+1÷12)÷X

Note that this program has been broken up into multiple lines for readability; on the calculator, it appears as a single formula line.