National Semiconductor 4615

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: Red  
    Display technology: Light-emitting diode 
Size: 6"×3"×1" Display size: 8 digits
Weight: 6 oz    
    Entry method: Reverse Polish Notation 
Batteries: 3×"AA" NiCd Advanced functions: Trig Exp 
External power: NS adapter   Memory functions: +/- 
I/O:      
    Programming model: Keystroke entry 
Precision: 8 digits Program functions:  
Memories: 1 numbers Program display:  
Program memory: 102 program steps Program editing: Step delete capability  
Chipset: National Semiconductor   Forensic result: 8.843762  

ns4615.jpg (25188 bytes)The 4615 is a somewhat unique member of the family of programmable LED calculators manufactured by National Semiconductor in the 1970s. The machine is functionally equivalent to the Novus Mathematician PR (4515) but its appearance is different; it also has no name, nor does it carry the Novus logo.

For some reason, this machine proved surprisingly difficult to find. I once bought one from a private collector in the US, but only an empty box arrived, courtesy of the United States Postal Service. Since another Novus calculator I purchased around the same time also got lost in the mail (and no other calculators did) I was beginning to fear that there is a curse, and I might never be able to complete my Novus/National Semiconductor programmable calculator collection.

Fortunately, another US collector recently came to the rescue, and sold me a working 4615 in very nice condition. At last, I also have an original Novus wall adapter! Not to mention a manual, which is of course quite nice to have...

Like the 4515, the 4615 has a crippled RPN model. A stack only three levels deep, the lack of a stack roll function, and a Z register that's filled with zero when the stack drops seriously reduces the utility of the calculator. Plus there's only one memory register, no control transfer instructions of any kind, and the biggest of all: no exponential display!

When I wrote the Web page for the 4515, I stated that this crippled programming model makes it impossible to create an accurate implementation of the Gamma function. That is not quite true; it is actually possible to use Stirling's formula to obtain the Gamma function to 7+ degrees of precision, utilizing only a modest number of the calculator's 102 program steps.

The program below actually calculates the Gamma function's natural logarithm, which is a far more useful function to have on a calculator that cannot handle numbers larger than 108. Oh, note that magic with entering 72 1/x 5 / instead of 360 1/x. For some reason, when you enter a 0 in a program, the machine interprets it as a halt instruction. Since I've noticed this behavior on the 4515 as well, I have to conclude that this is a known fault (feature?) of this machine.

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