FAQs Numbers 00 to 09

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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*Name*	*Aplet*	*SYMB view*	*PLOT SETUP view*
*Life's* *pretty* *straight* *without....*	Parametric aplet	X1(T)=3(SIN(T)+0.5COS(3T)) Y1(T)=3COS(T) Try changing the coefficents to get other interesting shapes.
*The Daisy*	Polar aplet	R1(Th)=3COS(5Th)+1 Can you get other flowers? What effect does the ratio 1:3 have?
*Christmas Tree #1*	Function aplet	F1(X)=X²*(X-INT(X)) F2(X)= -F1(X)
*Christmas Tree #2*	Function aplet	F1(X)=X*(1+INT(10/X)-10/X) F2(X)= -F1(X) This one looks ordinary until you zoom in on the area near zero. Try it - it's almost a fractal in it's infinite detail!

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.

Note: this is obviously out of date now! :-)

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

This should be rare on an HP39G, 40G, 39g+, 39gs or 40gs. On the HP38G it was very common but the later models have 232Kb, which should be sufficient for any normal use. The information below is really aimed at 38G users. There are a number of reasons that low memory 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 SHIFT CLEAR in the HOME view.
If you have a 40G or 40gs then you may be having problems because the CAS History has become too large. Like the HOME view the CAS maintains a record of all its commands and results, accessed by pressing SYMB. The memory consumed by this is listed in the MEMORY view (SHIFT MEMORY). If it is more than 10 or 20Kb then it is a good idea to delete it. In the CAS, press SYMB to enter the CAS History then press SHIFT CLEAR.

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. The 232Kb available in most models should be more than sufficient that this should not occur. You can store the equivalent of about 70 A4 pages of text in that amount of memory!

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 SHIFT PROGRAM to see the list of programs currently stored on your calculator. 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 .TANG.S, .TANG.PLT, .TANG.LIN etc. To delete a program, move the highlight onto it and press DEL. Alternatively SHIFT CLEAR will delete all of them but be careful you're not deleting programs you want to keep. 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. You can't delete this.
Note: The original design called for these support programs to be automatically deleted when an aplet is deleted in the APLET view but this doesn’t happen (a bug in the calculator that just never got fixed even in later models) so when an aplet is not needed any more you need to (i) delete it in the APLET view and (ii) delete any associated programs in the Program view.
On later models this should not be a problem from the point of view of using memory. However, the clutter they cause is annoying if you're trying to find a program you've created yourself and you may wish to delete them.

Other methods of clearing memory include:

Change to the LIST view (above key 7) and press SHIFT CLEAR to delete all lists.

Ditto for the Matrix view, the Notepad view (see "How can I save my notes?").

RESET any aplets not in use.

Perform a warm boot using ON+SK3 (see instructions). This clears the HOME history but nothing else

Perform a complete reset using ON+SK1+SK6 (see instructions). This clears ALL user data and resets the calculator to its factory settings.

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 highlighted in the APLET view and then press SHIFT NOTE (not SHIFT NOTEPAD) or SHIFT SKETCH.

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 Notepad view. Press SHIFT NOTEPAD to view the contents of this Catalogue. These independent Notes can be used to store information such as formulas or study notes.

The Notepad view has its own SEND and RECV buttons, which means that these Notes can be copied from one calculator 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 all the 39/40 series 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 is 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 is enabled are calculated from the function 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.

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 calculator 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 second page of the PLOT SETUP view (press the screen

button). 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. The default for this setting is to be switched on; you may find that, like me, you like it better switched it off!

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 two function values and the difference between the two functions. If the two values bracket the intersection, then this difference 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 all later models.
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 Format and 4 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 later models 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 your calculator 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 SHIFT CHARS and move the highlight to the character that you want. Two more pages are available by pressing

. 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.

On the 38G there was, I suspect, a problem somewhere deep in the innards of the calculator that caused problems with some programmed aplets when they have been run a number of times. It only occurs very rarely on later models but it was not uncommon on the 38G. 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 briefly see a copyright screen and then find yourself in the HOME view with the History having been cleared. Very occasionally you'll find that you get a screen full of strange characters. Just do it again.

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 and later models 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 later models you have to release SK6 first before releasing SK1 in order to reset. If you release both at once then it may still reset but it might 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.

Note 4: If you press ON+SK2 instead of SK3 then you will be put into diagnostic mode. This is a mode that the engineers can use to test a faulty calculator. Feel free to experiment with it. To exit, just do an ON+SK3.