Casio FM-300

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: Alphanumeric display  
New price:   Display color: Black  
    Display technology: Liquid crystal display 
Size: 4½"×2¾"×½" Display size: 8 characters
Weight: 2 oz    
    Entry method: Algebraic 
Batteries: 1×"CR-2016" Lithium Advanced functions:  
External power:   Memory functions:
    Programming model:  
Precision: 8 digits Program functions:  
Memories: 8 numbers Program display: Formula display  
Program memory: 76 program steps Program editing: Formula entry  
Chipset:   Forensic result:  

What a delightful find! For the first time in years, I discovered a truly unique programmable calculator on eBay, not like any I have previously seen.

The Casio FM-300 is a small, folding style calculator that looks rather unassuming at first: indeed, it looks like a basic 4-function calculator with square root.

But look more closely on the right-hand side. Are those touch keys? Is that a program run/write key? Three program areas? Even some rudimentary editing capability?

Indeed that's precisely what those buttons are. Which makes the FM-300 one of the rarest kinds of programmables out there: a programmable calculator that is not a full scientific calculator.

The FM-300 is called a "formula memory" calculator, but it really isn't formula programmable. Enter the program "2+3×5=" and the result you get is 25; clearly, the "formula" is just a sequence of keystrokes.

Nonetheless, even in the absence of higher mathematical functions, this calculator is capable enough to store a small program that uses Stirling's formula to compute the factorial/Gamma function of its argument:

MR x2 1/x ÷ 3 . 5 − 3 0 1/x ÷ MR x2 + 1 2 1/x ÷ MR + 1 × 
(MR ÷ 2 . 7 1 8 2 8 1 8 xy MR) × ( 2 × π × MR ) √ =

To run the program, just store it in, e.g., P1, then store the argument in the calculator's memory and press P1 in run mode. Alternatively, replace all occurrences of MR with A in the above, and allow the calculator to prompt for the value of the variable A.