00. Do you have any interesting graphs that you've found?

You might like to try graphing some or all of these. Jim Donnelly, one of the designers of the calculator's BIOS, created a Curves Collection of interesting curves which can be graphed on the 38/39G.  This is now maintained on my site since Jim moved on to other interests.
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01. Why have some of my keys stopped working?

Some of the early HP38G’s developed a fault whose symptom is that whole rows or columns of keys stop working. This is a warranty fault and HP are being very good about it, sometimes even if it occurs outside the warranty period. In Western Australia, contact Bookland on 9328 3966.
 

02. My calculator keeps telling me that I’m low on memory.

This should be rare on an HP39G, given that it has 232Kb of user memory.  On the HP38G it was very common. There are a number of reasons that it can occur. These include…

• not clearing your History.

The HOME view stores all your calculations so that they can be re-used. This consumes quite a lot of memory. It is a good idea to clear the History regularly by pressing BLUE CLEAR in the HOME view.

• accumulating too many Notes 
  (see "What's the difference between Notepad and Note?")

Although it is tempting to accumulate more and more notes that can be used in your various tests and exams, eventually this will cause problems with aplets. It is best to periodically dump them onto a computer using the Connectivity Kit. That way you can clear the calculator's memory if necessary without worrying about losing work.

• left over programs.

When you load aplets onto your calculator they often come with "attached" programs to do the work. These are stored in the Program Catalogue. Press BLUE PROGRAM to see the catalogue of programs currently stored on your machine. Generally these are named so as to make it clear which aplet they belong to. For example, an aplet called TANGENT LINE might have programs called .TAN.S, .TAN.PLT, .TAN.LIN etc. To delete a program, move the highlight onto it and press DEL. Alternatively BLUE CLEAR will delete all of them. In case you're wondering, the program called Editline, which doesn't delete, contains a copy of whatever you last typed in the HOME view. This is so that if you hit ENTER again it can be re-executed.
Note: The original design called for these support programs to be automatically deleted when an aplet is deleted in the LIB view but this doesn’t happen (a bug in the calculator) so when an aplet is not needed any more you need to (i) delete it in the LIBrary view and (ii) delete any associated programs in the Program Catalogue.

Other methods of clearing memory include:

• Change to the LIST Catalogue (above key 7) and press BLUE CLEAR to delete all lists.
• Ditto for the Matrix Catlogue, the Notepad Catalogue (see "How can I save my notes?").
• RESET any aplets not in use.
• Perform a warm boot (see instructions).

03. What’s the difference between NOTEPAD and NOTE?

Every aplet comes with its own attached Note and Sketch. When you copy the aplet to another calculator these are carried with it. They are usually used by the designer of the aplet to store instructions on how to use it. To see an aplet’s Note or Sketch (if it has one), make sure the aplet is higlighted in the LIB view and then press BLUE NOTE (above VAR) or BLUE SKETCH (above MATH).

In addition to these attached Notes and Sketches it is also possible to have independent Notes which are not attached to any particular aplet and which are not deleted when aplets are deleted. These are stored in the Note Catalogue. Press BLUE NOTEPAD (above 1 key) to view the contents of this Catalogue. These independent Notes can be used to store information such as formulas or study notes.

The Notepad Catalogue has its own SEND and RECV buttons, which means that these Notes can be copied from one 38G to another. See also How can I save my Notes?

04. Why does the default screen for the PLOT view have such a strange set of axes?

The screens on the HP38G and HP39G are 131 pixels wide by 64 pixels tall. A pixel ('picture element') is a single dot on the screen. No doubt there were good reasons in the design process for choosing these figures but for you and me it means that the best scales to use are ones which take these numbers into account. The default screen is -6.5 to 6.5 on the x axis. If you include the dot for zero, this means that there are 131 dots with each dot on the screen being 0.1 on the x axis. The advantage of this is that when TRACE and (X,Y) are in use in the PLOT view the cursor jump sizes are "nice" numbers. The y axis is not as important, since the (X,Y) values quoted at the bottom of the PLOT screen when TRACE and (X,Y) are enabled are calculated from F(X) anyway. The default y axis has the same jump size of 0.1

When you are planning your choice of scale in PLOT SETUP it is a good idea to use multiples of this default scale. For example, rather than using -10 to 10, use -13 to 13 (double 6.5). If you need to see 0 to 20, then choose -2 to 24 instead (which is -13 to 13 moved right by 11). If you don’t like having your scale end at "nasty" numbers like 6.5 then add 0.5 to both ends, changing -6.5 to 6.5 into -6 to 7.

A really good reason for doing this can be seen if you graph the function F1(X)= Sqr-root of (9-X²) using the scale of -3.5 to 3.5 on the x axis and the same on the y axis. If you graph this in the PLOT view you will see that the two ends of the circle nearest the x axis are missing. The same thing will happen if you graph a plain square root function. The reason for this happening with the circle is that the choice of scale means that the edges of the circle at -3 and 3 don’t fall on positions for which F1(X) is calculated. A better choice would have been -3.25 to 3.25, which is half of the default scale and thus has jump sizes of 0.05. If you try that scale you will find that you get the full half circle. An aplet called FUNCTION PLUS is one of the aplets in my set of Maths aplets. It is identical to the normal Function aplet but includes an extra option on the VIEWS menu under Autoscale called ‘Window Fix’. If you choose this option then the PLOT SETUP will be altered to find the closest scale to the one you have chosen which will has ‘nice’ jump sizes. If you don't want the memory overhead of an entire aplet then download the aplet, and delete it in the LIB view. This will leave the program called .FN+.WIN still available in the Program Catalogue. The only drawback is that every time you want to use it you'll have to change into the Program Catalogue, move the highlight to that program and press RUN. On the other hand, if you do it this way then it will work with any aplet rather than just Function.  Alternatively, just use manual methods in the PLOT SETUP view.

See also, how to get 'nice' values in the Plot-Table view.  See also, problems with graphing circles.
 

05. What does ‘Faster’ mean in the PLOT SETUP view?

When the 38/39G is drawing graphs it does it by calculating a y value for each horizontal dot position on the screen and then "joining the dots". When you choose ‘Faster’ the calculator only calculates every second dot along the x axis. For most graphs, which are relatively smooth, this will not matter and will result in a faster PLOT. On some graphs it will cause problems - see Why does the default screen for the PLOT view have such a strange set of axes? If speed is important then switch on SIMULT in the PLOT SETUP. This causes multiple graphs to be drawn simultaneously instead of one after the other. It's not as easy to tell which is which but it is definitely faster.
 

06. What does ‘Build Your Own’ mean in the NUM SETUP view?

This can be quite useful. Normally the NUM view is a simple table, with the starting value and the step size controlled by the values in NUMSTART and NUMSTEP. If you want to use your own values for x rather than just accepting these values then change NUMTYPE from ‘Automatic’ to ‘Build Your Own’ and then just type in any values for which you want the function calculated.

For example, if you were told to find the intersection of two graphs using the Bisection method and were required to show working, then enter the first function into F1(X), the second into F2(X) and then enter F2(X)-F1(X) into F3(X). Now change to NUM SETUP and change 'Automatic' to ‘Build Your Own’. Finally, change to NUM view. Enter two values for x which bracket the intersection point (presumably you know these already or can get them from the PLOT view). The third column contains the difference between the two functions and, if the two values bracket the intersection, should have a positive value for one x and a negative for the other. You can now enter further x values which gradually zero in on the intersection to the required degree of accuracy.
 

07. I have set ‘Fixed 2’ in MODES but this only works in the HOME view. Why?

Note:  This problem occurs only on the HP38G.  MODES works differently on the HP39G.
Yes - it’s a pain isn’t it! On the HP38G, the MODES view only controls the HOME view. Each aplet has its own setting for angle type and numeric type and these are not inherited from the HOME view. If you are having trouble with axis labelling in the PLOT view then the simplest way to fix it is to alter the settings in PLOT SETUP to better values.

If it is particularly important to keep your current settings then (i) make sure the aplet is highlighted in the LIB view, (ii) return to the HOME view and type Fixed<STO>Format and 4<STO>Digits. This will set the aplet numeric format to ‘Fixed 4’ but it doesn't take effect until you save the aplet under a new name (a bug in the HP38G). So now go the the LIB view and save the aplet under a new name.  If you now PLOT or SHOW something within the aplet the ‘Fixed 4’ setting will be used. This doesn't affect the numeric format in the SYMB view.

This problem has been fixed on the HP39G by tying the MODES view to the aplet and to HOME.  This means that the settings for the aplet and the HOME view always match and a change in the MODES view changes both.  It also means that changing aplets may result in a change to the angle and numeric settings and this is why on the HP39G the name of the aplet always appears at the top of the HOME view - to remind you of this possibility if you change aplets.
 

08. How do I get these weird characters that appear in various places?

The A..Z key can be used to get the letters of the alphabet. If you want any additional characters, these are available through the CHARS button. Press BLUE CHARS (above left bracket) and move the highlight to the character that you want. Two more pages are available by pressing PAGE DOWN. Pressing OK will transfer the highlighted character to the cursor position. More than one character can be transferred by pressing ECHO on each one and OK on the last.
 

09. My aplet used to work but now keeps giving strange error messages.

I suspect that there may be a problem somewhere deep in the innards of the calculator that causes problems with some programmed aplets when they have been run a number of times. If you start getting error messages offering to let you ‘Edit program’ then DON’T! There is a way of doing a "sweep out" of the memory of the calculator which seems to reliably fix the problem. This is called doing a soft reset or soft reboot. Hold down the ON key and then, while holding still it down, press (and hold) the third screen key. Hold the two buttons down for a moment then release them.

When you do this you should find yourself in the HOME view with the History having been cleared. On the HP39G you will see a momentary display of a copyright screen. If you now run the aplet again you will often find that the problem is fixed.

Note  1: There is another version of this called a hard or full reset which uses the first and sixth screen keys (HP39G users see note 2). DO NOT do this unless you are sure you don't need anything stored on the calculator! If you do it then you will find that the calculator's memory will be completely wiped, resetting it back to the default values it had when you first opened the box. Personally I do this fairly regularly anyway - it clears the system out completely. It doesn't erase the normal aplets, just resets them back to factory defaults.

Note 2:  On the HP39G the full reboot is a little harder to do (for increased safety).  On the HP38G you just had to hold down the ON button and press the first and sixth screen keys (SK1 and SK6).  On the HP39G you have to release SK6 first before releasing SK1 in order to reset.  If you release both at once then the calculator will go into diagnostic mode and the screen will fill with all sorts of strange stuff.  If this has happened to you, do an ON+SK3.

Note 3:  If your calculator has locked up so that the keyboard is not responding then try turning the calculator over and looking for a small hole.  If you unbend a paper clip and poke it into this hole you will feel a small button which you can press (gently).  This is the equivalent of doing a soft reset using ON+SK3 and you will hopefully find that this will unlock it without losing any memory.  It's worth a try.