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(2012-10-08)  
A flag  is a single bit that rules the machine's future behavior.

Flags are typically global  variables whose state can beread in all of the machine's otherwise secluded software environment (it's usually not recommended to have several separated program share thesame global variables). The meaning of each flag must be carefully documented and can be thought asa different yes/no option in the way the calculator will run.

The hp-48gII / hp-49g+ / hp-50g  calculators provide 256 standard flagseach identified by a number between -128 and +127. The negative-numbered flags are known as "system flags" and each describea particular "mode" that changes the way certain built-in functions behave. User-defined functions and programs may read those flags to adjust their ownbehavior accordingly, if needed.  However, it's not recommended thatuser procedures change system flags  (although it's tecnically possible todo so).

For a set of user-procedures to operate in different "modes" that can befreely modified, the so-called "user-flags", numbered from 0 to 127, can be used.

Traditionally, the low-numbered flags  (0 to 9, say) have no long-term function and canbe used by program segments for their own internal logic needs (it's assumed that two such program segments never run in parallel on thesame machine and that system procedures that can interrupt the execution ofothers never make use of those "temporary" flags).

How my recommendations differ from factory settings

Number		Description  ( &  motivations )
	-3	Numeric mode off  (don't evaluate symbols until so requested)
	-27	Disallow (x,y) format for complex numbers.
	-34	Print via IR  (to use the HP 822840Bprinter)
	-62	User keys on  (rather than "off")
	-95	RPN mode  (rather than "Algebraic mode")
	-103	Complex on  (rather than "Complex off")
	-105	Exact mode on  (instead of "Approximative mode on")
	-114	Display  1+x  (lowestdegree first)
	-117	Soft MENU  (rather than "CHOOSE boxes")
	-128	Complex variables allowed  (sure!)

The minor downside in the last choice is that the realand imaginary parts of the expression  A+i*B aren't necessarily  A  and  B,  respectively. A small price to pay for the freedom of being able to use  Z as a complex variable...

Among the unfortunate choice of nomenclature in the buit-in software, is the term "Fraction mark"  (flag -51 or "FM" choice in the top MODE meany/) to designate what ought to be called a "radix mark" (you have a choice between "radix point" and "radix comma"). In the usual decimal system of numeration, the radix is ten and whatwe're discussing is the  (cultural) choice between using either a "decimal point"or a "decimal comma".

(2012-09-28)  
Advanced calculators assign more than one function to most keys.

On the keyboards of basic calculators, every key is assigned one andonly one use, digit entry, binary operation (plus, minus, multiply or divide) orunary operation (typically, only the square root function is provided onsuch calculators).

Scienfific calculators provide so many functionsthat several uses must be assigned to a single key. The additional functionalities are typically accessed by pressing a specialcolored key before punching the key  (whose extra functionality may beindicated by a label of the same color either on the key itself or nearbyon the faceplate).

The hp-50g has three modifier keys at the bottom-left corner of the keypad:

• A topmost yellow ALPHA key.  (It's black on the "blue HP-50g").
• A first SHIFT key  (left shift)  which isblue on theHP-49 and white ontheHP-50  (it's light-blue with the blue faceplate).
• A second REDSHIFT key  (right-shift) which is red on both calculators  (orange with the blue hp-50g).

39 ordinary keys are thus given a total of 117 functions with the presenceof the two "shift" keys. The yellow ALPHA modifier key only pertains to the 26 keys whose top ismarked with a yellow letter of the alphabet. The lowercase version of those letter is obtained by pressing the SHIFT (left-shift)  modifier after  the ALPHA key.

For 21 of the alphabetic keys, pressing the REDSHIFTmodifier after the ALPHA key yields a special symbol, according to the following:

A	B	C	D	E	F	I	M	N	O	P	Q	R	S	T	U	V	W	X	Y	Z
						|			'		^						=	<	>	/

The 6 keys in the top rows are "soft menu" keysthat behave differently with respect to the shift keys. A white SHIFT stores the top of the stack into the variablewhose name appears above the key on the screen. A REDSHIFT puts the stored value of that same variable on top of the stack.

Because of that functionality, the 6 operations printed in white above thetop keys are accessed in a particular way, by holding down thewhite SHIFT key while pressing the desired top key.

Encoding of every key of the keypad

The function WAIT is located at PRG+NXT/IN.  It takes a single argument (-1 or 0,depending on whether the display of the current menu is requested or not)and waits till a key  (other than a modifier)  is pressed and released.

Among other things, WAIT is a useful function to experiment with just beforeyou intend to redefine a key for your own specialized usage, since WAIT  will confirm flawlessly the "code" you need to redefine thatparticular key for whatever specialized usage you see fit.

WAIT returns the decimal code of the key you pressin the format  rc.s  where "r" is the rowposition on the keypad  1 is the toprow, 10 is the bottom one) and "c" is the number of the column  (1 is the rightmost column) ranging from 1 to 6 for the top three rows and from 1 to 5 for the lower partof the keypad.  The "up" round key is at position 25 (positions 24 and 26 areempty and the 3 other round cursor keys are considered part of the third row: "left" is 34, "bottom" is 35 and "right" is 36. The decimal part of the keycode indicates its shift state

The 11 possible shift-states (.ss)in a keycode (rc.ss)

.s	Shifted		.s	Held shift
.00	Unshifted		.01
.10			.11
.20	Left-shift		.21	Held left-shift
.30	Right-shift		.31	Held right-shift
.40	Alpha		.41	Held Alpha
.50	Alpha + left-shift		.51	Alpha + held left-shift
.60	Alpha + right-shift		.61	Alpha + held right-shift

This leaves so many combinations that some of them are either undefined or undocumented.

Customizing the Keypad

The HP-49g+ / HP-50g calculators allow the user to define or redefine the function ofalmost every key  (the modifier keys are an exception).

Here are some keypad combinations that have no standard definition  (documented or not) at least in the 2.15 version of the software (2009):

• 25.2 (shifted up-arrow).
• 34.2 (shifted left-arrow).
• 34.3 and (redshifted left-arrow).
  (For these round keys, holding a shift key or not does notmake any difference; the codes 25.21, 34.21 and 34.31 are thus not available.)

You may want to try this feature first by assigning functions tocombinations that do not have a standard definition.

If you mess things up, you may always cancel "user mode" by doing a "warm start"to disable (temporarily) all the customized key definitionand regain the built-in functionality of your calculator to clean up thedamage before entering "user mode" again. To do a "warm start":

• Press the ON/CANCEL key (at the lower left of the keypad). Don't release it yet!
• Press and release the F3 key (third from the left in the top row).
• Release the ON/CANCEL key.

Knowing how to recover from catastrophic mistakes,we may now redefine a few keys with some peace of mind... (There are also commands intended for people who want to redefinethe entire leypad.  I won't discuss those.) For example, to let the shifted up-arrow give the number of thecurrent menu, do:

«  RCLMENU  »   25.2   ASN

To havethe left arrow call a menu by number when left-shifted, do:

«  MENU  »   34.2   ASN

To also make that same key conjure up the  PRINT  menu (describednext) when redshifted, do the following:

«  107   MENU  »   34.3   ASN

To view those three key definitions  (and other active ones, if any)  do:

RCLKEYS

To cancel the first definition, say, you may execute:

25.2   DELKEYS

To cancel all  key definitions, do:

0   DELKEYS

If you experiment a lot  with this feature, be aware thatdefining a key and cancelling its definition individuallywill waste a few bytes of memorythat are not reclaimed until the whole thing is cleaned up (by executing  0  DELKEYS). To clean-up while preserving all your definitions, do:

RCLKEYS   0   DELKEYS   STOKEYS

The number of the menu related to keypad manipulationsis  67.  If you've defined the keys as above,you may navigate to it in  3½  keystrokes!

(2012-09-22)  
The standard printer for recent HP calculators was introduced in 1989.

The original HP-49g  (1999) was powered by the same 3.68 MHz Yorke  chip (nativeSaturn architecture) as the earlier  HP-48gx, HP-48g, HP-38g and HP-39g. The single high-power pin of that chip (used for IR transmission by those other calculators)  was needed forthe write mode of the flash memory which the HP-49g was the first to offer. Therefore, the HP-49g had no IR capability at all.

The HP-49g+ (2003) and HP-50g (2006) are based on completely different hardware (whereby the Saturn CPU is emulated by a RISC processor)  and they do offer IRcommunications at low power  (limited range).

The outgoing IR beam is in the middle of the forward panel,at the location indicated by the small forward-pointing triangle printed on the faceplate. This arrow should be aligned with the IR input port of the HP 82240B printer (to the left ofthe red power indicator). For reliable transmission on battery power, it's best not to exceeda separation of one inch between the two!

When the calculator is powered by a USB cable,  the distance can be up to six inches or so (a good thing, since two inches of forward clearance are needed toplug in the straight USB cable which comes with the HP-50g).

Printing outdoors, or in bright light, can be a problem (if so, shade the space between the printer and the calculator with a piece of cardboard).

The calculator's flag -34 must be cleared  (unchecked) to read  "Print via IR"  instead of "Print via wire"  which is the default factory setting. For test purposes, use either  PR1  or  PRST  with a single number on the stack.

HP-49g+ / HP-50g System Flags Related to IR Printing

Number		Description  ( &  recommended setting )
	-33	Transfer via wire  (irrelevant to IR printing)
	-34	Print via IR  (MUST be clear/unchecked)
	-35	ASCII transfer  (default setting = clear/unchecked)
	-37	Single-space print (check if double-spacing is desired)
	-38	Add linefeeds  (default setting = clear/unchecked)

All the print-related functions are described below. In particular, the following sequence of commands displays a plot of the current equation  (if there is one) and sends it to the printer:

« ERASE  DRAW  PRLCD »

The value of the reserved variable  PRTPAR  is a list four parameters that can be resetto the following default settings by purging it:

1. Print delay.  Normally set to  0.  Modified by the function DELAY.
2. Character remapping string, set by default to the empty string. The empty string  (no remapping)  is appropriate for the newer  (1989) HP 82240B  printer. To use the previous  (1986) HP 82240A,  the remapping string should be set to the proper (complicated)  value by executing the OLDPRT  command  (whose effect can be undoneby purging the entire PRTPAR variable). Even so, there are  24 special characters that the old  HP 82240A  can't handleproperly  (they will be printed as checkered rectangles).
3. Line length.  Normally set to 80.
4. line terminator string.  Normally, a two-character string  (LF & CR).

(2012-09-28)  
Do not confuse positive infinity  (+, "Shift-0", real) with the unrelated unsigned infinity  (, 1/0, complex)!

The only algebraically-defined infinity  (i.e., 1/0) is the unsigned infinity  ,  at the "horizon"  of the planeofcomplex numbers.

It verifies the following relations, for any finite nonzero complex number  z :

z .   =         .   =        z /   =   0     z / 0   =  

The following expressions are explicitely undefined :

0 / 0     0 .       +

Adding two signed infinities   and   on either side of the  (open) real line  form what's called the closed real line. Those two are not  defined algebraically but as the conventional results of somelimiting processes.

In particular,   isn't equal tothe aforementioned unsigned infinity   (the "plus sign" is not  optional).  We have     =   (-1) ()  and:

()()   =         + ()   =         + ()   =  

The following relations hold for any nonzero real  x  and any positive  y:

+ x   =         . y   =        x / ()   =   0
+ x   =         . y   =        x / ()   =   0

The following expressions are undefined within the closed real line :

+ ()      . 0      . 0     x / 0  (for x finite or infinite)

With one caveat which shall be discussed shortly, the three types of pseudo-numerical infinities are perfectly implemented on the HP-49 series,in accordance with the above rules. (Not so with theTI calculators reviewed elsewhereon this site, which merge positive infinity and unsigned infinity into one singleill-defined entity, with unacceptable results.)

The keyboard  (SHIFT 0) gives positive infinity ()  and it can be changed to negative infinity  () with the (+/-) key  (located above the "7" key). The unsigned infinity  () is best obtained as the result of 1/0.  Note that:

ATAN()  =  /2         ATAN()  =  /2         ATAN()  =  ?

The calculator uses the symbol "?" to indicate explicitely an undefined result.

P(x)   =  _na_n xⁿ

(2012-10-07)  
It's not possible to define other ones.

The first thing is to observe the location of the underscore character on thekeypad.  Its code is 75.3.  That means it's located on the seventhrow  (from the top)  and the fifth column  (from theleft)  with a right-shift  (that's what ".3" means).

Numbers with physical simensions are ordinary real numbersfollowed by a suffix consisting of an underscore character followed bythe name of a physical unit which can be either its predefinedabbreviation with or without an exponent  (the "^" characteris obtained by pressing the first key of the fith row)  orany multiplicative expression of such  (using parenthesesand the operators "^", "*" and "/"). The following units are avalaible in the various submenus of theUNITS menu:

Length:   _m  _cm  _mm  _yd  _ft  _in  _Mpc  _pc  _lyr          _au  _km  _mi  _nmi  _miUS  _chain  _rd  _fath          _ftUS  _mil  _µ  _Å  _fermiArea:     _m^2  _cm^2  _b  _yd^2  _ft^2  _in^2  _km^2          _ha  _a  _mi^2  _miUS^2 _acreVolume:   _m^3  _st  _cm^3  _yd^3  _ft^3  _in^3  _l          _galUK  _galC  _gal  _qt  _pt  _ml  _cu  _ozfl          _ozUK  _tbsp  _tsp  _bbl  _bu  _pk  _fbmTime:     _yr  _d  _h  _min  _sFrequency:  _Hz      (at the end of the "Time" menu)Speed:    _m/s  _cm/s  _ft/s  _kph  _knotAcceleration:  _ga   (at the end of the "Speed" menu)Mass:     _kg  _g  _lb  _oz  _slug  _lbt  _ton  _tonUK          _t  _ozt  _ct  _grain  _uBulk:     _mol        (at the end of the "Mass" menu)Force:    _N  _dyn  _gf  _kip  _lbf  _pdlEnergy:   _J  _erg  _kcal  _cal  _Btu  _(ft*lbf)          _therm  _Mev  _evPower:    _W  _hpPressure: _Pa  _atm  _bar  _psi  _torr  _mmHg          _inHg  _inH2OTemperature:  _°C  _°F  _K  _°RElectrical:   _V  _A  _C  _Ω  _F  _W          _Fdy  _H  _mho  _S  _T  _WbAngle:    _°  _r  _grad  _arcmin  _arcsSolid angle:  _sr    (at the end of the "Angle" menu)Light:    _fc  _flam  _lx  _ph  _sb  _lm          _cd  _lamRadiation:  _Gy  _rad  _rem  _Sv  _Bq  _Ci  _RViscosity:  _P  _St

Except for four headings  ("Electrical", "Light", "Radiation" and"Viscosity")  the above list regroups under the same headingunits of the same physical dimension. (The list has the same structure as the UNITS submenus on the calculator, except as noted.) To express a dimensioned quantity in compatible units, one feeds it asthe first argument of the  CONVERT  function which receives assecond argument any quantity  (whose magnitude is ignored) expressed in terms of the desired target unit.

To have the result expressed in compatible standard SI units,one uses the function  UBASE  (which takes a single argument). Unfortunately, this breaks SI units down to their MKSA componentsand yields unit combinations that may not be easily recognizable,especially in the case ofelectromagnetic units... The function  UFACT  can be used to collapse "manually"the units of one quantity in terms of a multiple of the other, butthat's a lot of trouble just to visually inspect the dimension of a result...

Physical units were first introduced by HP with the HP-28 handheld calculatorsback in 1986  (along with the first public version of their RPL language). Surprisingly enough, their "precise" definition of the year as a unit oftime was erroneous then and it remains erroneous now, nearly 30 years later. Not only is it wrong in HP calculators but it's also wrong in handheld calculatorsbyother manufacturers, who have mindlesslycopied HP's mistake.  For the record:  The only  scientific definition of the year  as a proper unitof time is 31557600 seconds (that's 8766 hours of exactly 86400 atomic seconds).  100 of thoseyears make, by definition, one Julian century, the unit of time commonly used by astronomers to describethe so-called secular variations in decaying periods within the solar system (including the mean solar day or the tropical year). Also, one light-year is defined as the distance obtained by multiplyingthespeed of light (Einstein's constant, c)  into this precise duration  (and no other).

No User-Defined Units :

The HP firmware doesn't provide any way to define specializedunits other than the predefined ones. If you owned a calculator descended from the TI 92 Plus  (the original TI-92 didn't support units at all) and were in love with thetypographical point (and/or the Didot point  a submultiple of the ancient pied de roi ) you could simply tell your calculator about it,once and for all in the following way:

0.013837 _in   _point

There's no way to do anything similar with an  HP-50g.

(2012-10-06)  
Severe problems and minor ones.

Unfortunately, like many other calculators,the HP-50g suffers from the annoying widespread prejudice against raisingzero to the power of zero (which is actually a perfectly well-defined operation whose result is 1). With all revisions of the HP-50g firmware  (at this writing) raising zero to the power of zero wrongly  gives an undefined result  (symbol "?").

Needless restrictions :

A number of functions which are either nonsensical or notoriouslyunpredictable in approximative calculations are only available in "exact mode".  For each of those, the reference manual warns us that:

Exact mode must be set (flag -105 clear).
Numeric mode must not be set (flag -3 clear).

So far so god, but we are also needless told that "radians mode must be set (flag -17 set)".  even in thosecases where angle measurements are irrelevant...  Indeed, the calculator willask you to leave the realm of angular degrees befor it allows you to performmodular arithmetic and the like...

This applies to the following functions, in particular:

ABCUV,ADDTMOD,COLLECT,DIV2, DIV2MOD, DIVPC,EGCD,FACTORMOD, FACTORS,GCDMOD,HORNER,IABCUV, ICHINREM, CHINREM, IEGCD, IQUOT, IREMAINDER,LCM, LGCD, MULTMOD,POWMOD, PROPFRAC,QUOT,REMAINDER,SUBST, SUBTMOD, TRUNC.

Formatrix and/orpolynomialcomputations that are also irrelevant to angle measurements,exact mode is, arguably, a needless luxury as well  (although correctapproximativecomputations are admittedly a major source od headache for system programmers). The above bug is thus combined by this wishful remark for:

AXQ, GAUSS, GBASIS,GRAMSCHMIDT, GREDUCE,CHOLESKY,JORDAN, LAGRANGE, MKISOM,PARTFRAC, PTAYL,QXA, REORDER, SYLVESTER.

"Not only the trigonometry rewriting operations, but some other CAS operations require the angle mode tobe set to radians (flag -17 clear), even if it is not immediately obvious that this is so. For this reason, theFlags section of many operation descriptions says that radians mode should be set"

(2012-10-14)  
Discontinuitycliffs appear in the complex extensions of some functions.

By default, electronic calculatorsdon't extend the domain or the range of real analytical functionsto thecomplex realm. With the HP-49/HP-50 calculators, complex calculations mustbe explicitely authorized by changing the factory settingofflag -103  (either directlyor via the CAS submenu from the MODE screen).

It's also recommended to clear manually the last systemflags (-128) to also allows variables to represent complex numbers. Beyond introductory or specialized calculations, there are indeed few advantagesin assuming that all variables are real (to state, for example, that the real part of the quantity a+ib  is always a ). For consistency, I recommend to set flag -27 as well (otherwise, some misleading output like  (a,b) could occur).

There'sno continuous wayto extend to the complex realm some quantities definedfor positive real numbers, including square-roots and logarithms.

Be that as it may, is not handling this particularmathematical situation nearlyas well as their historical competitor  (whoseconsistent approach is reviewedelsewhere on this site with a discussion of the relevantmathematical issues).

Although HP probably didn't design this strange behaviorintentionally, the way they implemented the square-root functionmakes it unusable whenever there is any chance thatthe argument will be a negative real number (complex numbers with a nonzero imaginary part seem to behandled correctly).

(2012-10-04)  
RPL officially meant ROM-based procedural language  (HP, 1986).

History :

RPLis a stacked-based programming language similar toForth. It originated in 1984 at HP's development facility of Corvallis  (Oregon) and has been supported by all main HP programmable calculator series since then: HP-28 (1987) HP-48 (1990-2003) andHP-49 series (1999)which includes the current HP-49g+ (2003) and HP-50g (2006).

The newest HP calculators are also programmable in the assembly language of theSaturn microprocessor (introduced in 1984 for theHP-71B, a BASIC-programmableupgrade to the legendary HP-41C).

Finally, the HP-49 and HP-50are based on a RISC processor which emulates the Saturn processor. They come with the "MDG Meta Kernel",a full programming environment which was once a costlythird party add-on, as advertised on the screenful at right (very briefly flashed every time a warm-start  is performed).

(2012-10-16)  
Documenting undocumented features.

It's a modern tradition by programmers of complex systemto add unofficial features whose convoluted mode of accessis spread by word of mouth among the community of users. Those are known as Easter eggs.

Here aresomeof the better known Easter eggs for the  HP-50g:

Collective signature of the development team:

Type in the word  RULES  on an  HP-50g and you'll see a crossword display of 26 words. This includes the acronym  ACO  which stands for Australian Calculator Operation the great HP design team that was formed in November 1997 anddisbanded in November 2001.Their greatest endeavor was the  HP-49  (of which the HP-50g  is a late incarnation).  That project's code name (VGER  or  V'Ger)  is found just below ACO.

The other words  (including "G.T.") are the first names or nicknames of the following 24 people,who were part of the adventure:

• Bernard Parisse. Erable. HP-49 Computer Algebra System  (CAS).
• Chris Leitao
• Christian Bourgeois
• Cyrillede Brebisson,  R&D engineer.
• Dan Smith
• David Chibo
• Gabriel Lagos
• Garry Heinze, HP Australia (1997).
• Geoffrey Marnell
• Gerald Squelart,French programmer.
• G.T. Springer,"Education Solution Architect".
• Jean-Yves Avenard.  HP48 Meta-Kernel (MK).
• Jeff Harcourt
• Jian He
• Keiran O'Neill,hardware engineering consultant.
• Mark Carter
• Mika Heiskanen. Jazz. HP-49 Computer Algebra System  (CAS).
• Mitch Davis.  Manufacturing.
• Nigel Hooke,Australian software designer.
• Peter Lanius, Ph.D.  (particle physics).
• Ray Suryn, software engineer.
• Rodolfo Sandonato,Australian engineer.
• Tanya Brooks. Product manager (sales/marketing).
• Tehn Yit Chin.

Press the  ON  key to go back to normal operations.

Possibly because his first name was too long, Claude-Nicolas Fietcher  isn't included in the above buthe is prominently credited in the following way:

Typing the word  VER  yields  (with the latest HP-50g firmwareat this writting)  a value of  4.20060919 and a two-line display at the top of the normal screen which says:

HP49 CAS by Parisse,Heiskanen & Fietcher

The official  VERSION  command puts two strings on the stack. One identifies the firmware version, the other is a copyright notice. Lately:

2: "Version HP50-C    Revision #2.15"1: "Copyright HP 2009"

PlayTetris ^® :

To bring up the game, with firmware above 1.18, do the following:

1. Enter the equation writer  EQW (3^rd key of 4^th row, redshifted).
2. Lock alphabetic entry mode  (press  ALPHA  twice).
3. Type the word  MINEISBETTER.
4. Exit alphabetic entry mode  (press  ALPHA  once).
5. Push the (round) up-arrow key to highlight the whole word.
6. Choose  SIMP  on the soft menu  (press last key of the top row).

The game is played by pushing  5  to rotate the current falling piece (push and relaease the "2" key to force it to fall one step downor hold 2 to make it fall very fast). Keys 4 and 6 move the piece left and right, respectively.

The object of the game is to form as many complete horizontal lines of squares(it need not be at the very bottom of the playing field,although it often is in normal play). Once a line is formed, it is deleted and and leaves more breathing room to play the restof the game. The shape of the next piece is previewed on the top right tohelp the player choose best tactics to position the current piece. The game ends when the playing field is so cluttered that new pieces can't even falldown a single step.

The game accelerates once 30 lines have been scored,which makes it much more difficult to play beyond that point.

There does not seem to be any way to exit a game except by playing it out (if need be, you can do that quickly by pushing and holding the "2" keyas pieces keep appearing). At that point, the score obtained  (number of horizontal lines completed) is shown as the "result" of what's formally the "simplification" of MINEISBETTER.  You can push that result to the stack by pressingthe  ENTER  key to return to normal operations.

If a key is depressed just after the game ends, it overwritesthe score which normally appears in EQW mode. If that happens, you may retrieve the score by pushing  UNDO (the  HIST  key redshifted). If that doesn't  happen,you may still want to push  UNDO  to cancel the resultof the last action  (namely, playing Tetris)  and justretrieve the name  MINEISBETTER  itself. If you do that,you just need to push  SIMP  again (soft label of the top-right key marked F6) to start a new game of Tetris, without any typing.

Play MineHunter :

This game was bundled with HP-48 calculators but not withthe early HP-49 calculators. Technically, it isn't an Easter egg  but a regular command,documented in the HP-50g reference manual  (Advanced User's Guide): MINEHUNT  (abbreviated MINEH)  is the first item in menu 117.

• Push the  APPS  key.
• Select the 12th choice  (Equation Library).
• Select the  UTILS  submenu.
• Select the first item in that menu.

Alternatively,  type  MINEHUNT  or retrieve that from the CATalog.

The game is played on a grid of 128 squares  (16 by 8). Starting at the top left corner, the object of the game is to reach the bottom rightcorner without hitting any of the hidden mines. The more squares you visit beforereaching the goal, the higher your score (the maximum score is normally 108, if you set to  n  thenumber of mines, it becomes  128-n). The game isn't timed.

You move using either the four arrow keysor the numerical keys surrounding the "5" key (the latter method is reguired to move diagonally).

There are normally 20 hidden mines, but this number can be changed by storing anyinteger from 1 to 64 into a variable called Nmines  in the current directory. If a negative number is used, the mines will be visible!

As you move about, you're told how many mines are "near" your current position (i.e., on one of the 8 adjacent squares).Collecting this information mentally is often (but not always)  sufficient to solve the entire game by pure logic,without taking any risky guesses.

When you've completed a game (successfully or not)  you may start a new one immediately by pressing  F1 (top-left-corner key). Press  ON  (bottom-left corner) at any time to quit playing without saving the current game.

You may also exit by pressing  STO  to save the current gameinto a variable called MHpar  in the current directory (next time  MINEHUNT  is executed,the game so saved will be loaded automatically from whatever directory is then current and the corresponding MHpar  will be PURGEd).