Tianyan Electronics TY-82MS-3

Datasheet legend
Ab/c: Fractions calculation
AC: Alternating current
BaseN: Number base calculations
Card: Magnetic card storage
Cmem: Continuous memory
Cond: Conditional execution
Const: Scientific constants
Cplx: Complex number arithmetic
DC: Direct current
Eqlib: Equation library
Exp: Exponential/logarithmic functions
Fin: Financial functions
Grph: Graphing capability
Hyp: Hyperbolic functions
Ind: Indirect addressing
Intg: Numerical integration
Jump: Unconditional jump (GOTO)
Lbl: Program labels
LCD: Liquid Crystal Display
LED: Light-Emitting Diode
Li-ion: Lithium-ion rechargeable battery
Lreg: Linear regression (2-variable statistics)
mA: Milliamperes of current
Mtrx: Matrix support
NiCd: Nickel-Cadmium rechargeable battery
NiMH: Nickel-metal-hydrite rechargeable battery
Prnt: Printer
RTC: Real-time clock
Sdev: Standard deviation (1-variable statistics)
Solv: Equation solver
Subr: Subroutine call capability
Symb: Symbolic computing
Tape: Magnetic tape storage
Trig: Trigonometric functions
Units: Unit conversions
VAC: Volts AC
VDC: Volts DC
Years of production:   Display type: Numeric display  
New price:   Display color: Black  
    Display technology: Liquid crystal display 
Size: 6"×3"×½" Display size: 10+2 digits and 14 characters
Weight: 4 oz    
    Entry method: Formula entry 
Batteries: 1×"AAA" alkaline Advanced functions: Trig Exp Hyp Lreg Ab/c Cplx Cmem 
External power:   Memory functions: +/- 
    Programming model: Formula programming 
Precision: 13 digits Program functions:  
Memories: 9 numbers Program display: Formula display  
Program memory: 79 program steps Program editing: Formula entry  
Chipset:   Forensic result: 9.000000002124  

Look what the cat, I mean the mailman, just brought in, straight from China.

A bona fide programmable (abeit just barely) calculator, bearing a superficial resemblance to numerous Casio models and lookalikes, yet a unique design.

The Tianyan Electronics (never heard of this manufacturer before) TY-82MS-3 is a no-nonsense basic scientific calculator, with formula entry, which is pretty much the standard these days.

But it is intelligently designed (e.g., permitting self-evident shortcuts, such as writing 2pi instead of 2*pi) and it does have a few non-trivial features, such as 13 digits of internal precision or the ability to do just linear but also quadratic regression.

And on top of all that... look, it has a LRN key!

And yes, the key signifies exactly what it should: programmability.

Very simple programmability, mind you. The LRN key simply allows the calculator to remember the most recently entered formula for later replay using the LET key. But the formula is stored in memory where it is retained even after the AC key is pressed or the calculator is turned off. Therefore, though not Turing-programmable (no jumps, no conditional execution, no addressable memory) it nonetheless qualifies as a bona fide programmable calculator.

To celebrate this discovery, here is my favorite Gamma function implementation for this calculator:

X ln X - X + ln √(2π÷X)+((((X²÷1188-1÷1680)÷X²+1÷1260)÷X²-1÷360)÷X²+1÷12)÷X