The PC-G850 can be nicely used as a calculator, albeit in BASIC, which is cumbersome.

Attached is an

RPN Complex Calculator I wrote that

emulates the HP-15C. The display shows the T,Z,Y,X stack and its "imaginary stack" S,K,J,I. All of the PC-G850 function keys work. Like the HP-15C it has complex arithmetic, 2-var statistics, STO/RCL registers, and can be extended with BASIC programs (see source code). I also threw in some extra features, such as rational approximation by continued fractions.

RUN to start, clears registers

GOTO*R to resume without clearing registers

Keys for operations and functions:

A abs, |XI| -> XI

C ceiling, ceil(XI) -> XI

E x10^ (when entering a number)

F fraction, frac(XI) -> XI

G GCD, gcd(Y,X) -> X

H hyp prefix to [arc]sin,[arc]cos,[arc]tan

I enter imag part / back to real part

J same as I (for engineers)

L linear regression, slope and intercept -> Y,X

M mean of y and x -> Y,X

N floor, floor(XI) -> XI

Q quotient and remainder of Y/X -> X,Y (quotient in X, remainder in Y)

R rational, X -> Y,X such that Y/X approximates the given X within 1E-10

S stddev Sy and Sx -> Y,X

T truncate, trunc(XI) -> XI

V variance of y and x -> Y,X

Y linear estimation of r and y given X=x -> Y,X

^ raise, YJ^XI -> XI

+ add, YJ+XI -> XI

- subtract, YJ-XI -> XI

* multiply, YJ*XI -> XI

/ divide, YJ/XI -> XI

! factorial/gamma, fact(X) gamma(X+1) -> X

% percentage, X/100*YJ -> XI

2ndF SHIFT

SHIFT does not operate

CLS clear entry

CA clear all, restart

SPACE (or SHIFT minus) change sign, -XI -> XI

ENTER push on stack

BS delete

LEFT delete

RIGHT swap XI with YJ

UP roll stack up

DOWN roll stack down

RCM last-x, push LM -> XI

S-CONST (SHIFT CONST) display registers (press key to continue)

CONST STO [+|-|*|/] #register (press digit, or op then digit)

ANS RCL [+|-|*|/] #register (press digit, or op then digit)

F<->E re<->im, swap X with I,

->DEG hh.mmss X -> degree X

->DMS degree X ->hh.mmss X

PI push pi -> X

RND random, push random 0<x<1 -> X

MDF round towards zero, round(XI) -> XI

STAT clear stat registers R2 to R7

M+ stat add Y,X (updates registers R2 to R7 as per HP-15C stat)

M- stat remove Y,X

= enter Basic expression

... any PC-G850 calculator function key such as SIN

The implementation attempts to avoid intermediate overflow and roundoff issues, e.g. Numerical Recipes and "What Every Computer Scientist Should Know About Floating-Point Arithmetic".

New and improved version: [attachment=8966] annotated with comments and [attachment=8967] without comments
To extend the program, for example to press Q to produce the quotient and remainder of Y/X, just add an entry for key Q (ASCII 81) line 181:

' Q quotient and remainder of Y/X -> X,Y (quotient in X, remainder in Y)

181 IF A=81 GOTO 1000

1000 IF I<>0 OR J<>0 OR X=0 OR X<>INT X OR Y<>INT Y OR ABS X>=1E10 OR ABS Y>=1E10 GOTO 15 ' error

1010 N=X,X=SGN X*INT(Y/ABS X),Y=Y-N*X: GOTO 40

Enjoy!