Free42 is a simulator (not an emulator) of the HP 42s, and it is a neat work.

This article is made as a byproduct of exploring the Free42 while trying to find out if the functions mentioned in the manual of the sharp el 506w (produced in the early 2000, the manual was made for 506w and 546w models), a scientific calculator not programmable and not graphing, are present on the HP 42s or better on the Free42. From now on the Free42 is mentioned as f42 or and the sharp el 506w is mentioned as 506w.

It is like an exploration by comparison and of course it will miss functions that are partially mentioned or absent on the sharp 506w. The same comparison can be made with other non-programmable non-graphing scientific calculators. Why scientific calculators? Because the HP 42s is advertised so, rather than being programmable.

Moreover the exploration may miss functions declared as “not there” but being implemented in the free42. Indeed it is an exploration.

During the comparison, some operations, assumed to be “common” would be skipped. The HP 42s (or Free 42) uses the RPN notation that is assumed known by the reader. If the reader does not know the RPN, nevertheless the examples here written (one should deduce the syntax thought) or the documentation provided by the Free42 homepage would be enough to master it. Also the 506w commands can be read on the manual, so I would post non-obvious procedures only for the F42.

On the 506w there is the possibility to do constant calculation. For example:

# finding multiples of 117 # one types 117 x 1 = 117 2 = 234 3 = 351 # adding a number to 63 5 + 63 = 68 8 = 71 4 = 67

The f42 achieve this with how the stack registers ( X, Y, Z , T ) are designed. In short, when numbers are entered they lift the stack, when they are “consumed” the stack drops replicating the last register, T.

typing: 117 enter enter enter (check with Rdown that the stack is full of 117) typing: 1 x res: 117 typ: 2 x res: 234 typ: clx 3 x res: 351 typ: 63 enter enter enter typ: 5 + res: 68 typ: clx 8 + res: 71 typ: clx 4 + res: 67 # actually with this operation we never activate the stack drop, # because we just used the register X together with Y but Y is not consumed. # This is how the CLX function works (or clx). # last X can be used to but in cooperation with drop of the register X # because if I type 63 5 + (= 68)and then last X without clearing X before # then 68 goes in Y. If instead I clear X, Y is not affected because the stack # list is disabled.

We have \( f(x) = x^2 \) so \( f'(x) = 2x \) , what about computing it in \( \sqrt{6} \) and \( 8 \) ?

# 506w typing: alpha X x^2 2ndF d/dx (typing the main function, not f') (answer to X?) sqrt(6) cannot be typed, so we type only 8. (answer to dx?) we leave default result = 16. Ok. # typing sqrt(6) using the variable A and then recalling its value when the question is asked res: 4.898979481 note that 2 * sqrt(6) on the calculator returns the same value.

Something a tad more difficult involving fractions \( f(x) = \frac{1}{3} \cdot x^{3} \) we should get \( f'(x) = x^2 \) , again in \( \sqrt{6} \) and \( 8 \) .

# 506w (typing 1/3 as fraction with the command "a b/c" ) # typing the main function, not f' result sqrt(6): cannot be typed. result 8: 64 , ok. # sqrt(6) stored in A and then recalled when asked. res: 5.999999989 (it should have been 6)

At the moment numerical differentiation seems not available as built in function in f42. Surely there exist a listing providing them (TODO: find them and showing how to integrate them), but the point that are not built in.

We integrate \( 1/3 \cdot x^3 \) between 5 and 12, then \( sin(x) \) between 0 and \( 2 \cdot \pi \)

#506w # 1/3 * x^3 # 1/3 typed as fraction of the type "a b/c" # n=100 # takes a bit res: 1675.916667 # sin(x) # 2*pi cannot be entered, so it is saved first in a variable, like A, then recalled. res: 0.344169068

Free42

# we have to program a function to make a numerical integration # a bit more tedious than the 506w, but it will be good to introduce some basic programming. # actually the solver allows constant in the integration, but this will be shown in another example # hopefully. #To start programming mode GTO .. # this creates a new program area (programs areas are delimited by a starting label and and END PRGM # the new program area is shown by a 0-byte program # END is shown, we will not have to type it when typing whatever program # # PRGM works also if by mistake one leaves the programming mode, typing it again # shows the current program PGM.FCN LBL # now we can name the program, max 7 characters. We need to select the chars # through soft menus # We want a function so "X3I" (enter to submit) arrow_down (for the next instruction) # (X^3 integral) # we need to name variables with MVAR for the solver # and those have to be declared right after the label shift intfx MVAR "X" EXIT arrow_down 1 arrow_down 3 division RCL alpha X 3 y^x EXIT # use PRINT PRUSR to see that the program is there. #now let's open the solver intfx X3I select X 5 LLIM 12 ULIM 0.001 ACC # pres the simbol of integral int res: 5027 # a bit off, something went wrong, let's check the program again. EXIT EXIT EXIT PRGM # review with arrows up and down # yes, the multiplication between 1/3 and x^3 is missing. # place the cursor where Y^X * EXIT # let's check that all is fine PRINT PRP X3I # check the printer output in f42 # Once again let's go to the solver intfx X3I X 5 LLIM 12 ULIM 0.001 ACC int res: 1675.9166667 ###### ###### # now we compute the sin GTO .. PRGM PGM.FCN LBL "ISIN" (enter to submit) arrow down (for the next instruction) shift intfx MVAR "X" EXIT RCL alpha X arrow_down SIN EXIT # use PRINT PRUSR to see that the program is there. #now let's open the solver intfx ISIN select X 0 LLIM 2 ENTER pi multiplication # showing 6.2831... now ULIM 0.001 ACC int res: 3.44169..e-1 # note: # backspace clears lines # inserting inserts program lines after the current program line visualized # so on line 3, if we type, we go on line 4.

Free42:

#Use the convert menu #it is possible to convert degrees to radians (and back), then hours-minutes-seconds (and back), #but no 400 degrees conversion, for that surely routines exists

The 506w has some single letter variables (or better, registers). Like a dozen of them.

Free42

# One can use named named variables up to seven chars 105 STO Alpha "t1" ENTER -50 ENTER # -50 now in register y RCL select T1 + res (in x) : 55 # storing in the register is the same of the named variables # only one has to type a double digit 00 to 24 (normal available registers) # What is interesting is to use one of the four stack register 105 STO . ST Z (the second last register, remember stack lift) 0 (stack lift) RCL . ST T (the last register, remember stack lift)

Free42

# we want to save the program pi * radius^2 # variable is the radius GTO .. PRGM PRGM.FCN LBL CAR (circle area) ENTER arrow_down x^2 #the program assumes the variable in register X PI multiplication EXIT # now executing with a radius of 5 5 XEQ CAR res: 78.53981..

shift clear CLST

(to access through the advanced options of Free42)

shift print PRP: prints a program, if not selected, the current. PRST: prints the stack (useful to visualize the registers) PRUSER: prints user variables and programs PRX: prints X register PRLCD: prints the actual content of the screen

- Free42
- Aup or arrow_up: arrow up
- Adown or arrow_down: arrow down
- Rdown: the command under the second mode PI, to roll down the stack.
- shift: the orange button. Activate second mode.
- clx: the backspace key, it works differently according to the context. Normally it clears the register X. In program mode deletes the current line of the program.
- intfx: the second mode over the key 8.

As usual the HP calculator communities produces several examples and interesting discussions (especially in discussion places like the forum of the museum of HP calculators). Please refer to this page for additional resources provided by the HP communities and feel free to expand it! The only problem, as usual in a discussion community, is that resources may be scattered. A wiki is a nice way to fix this, just with a collection of links :)

Other resources related to the HP 42s or Free42 are directly on the Free42 page.

# a scan of the 42s manual on the ed2k network since it is not provided by HP anymore. ed2k://|file|manual-hp42s-us.pdf|36139161|2CD2362840E0440E44A58C1BE8045960|h=YK5XKJDVVIGCLER4SSWPAUQJIPRQCXC7|/ # a scan of programming examples. ed2k://|file|hp42s-programming-examples.pdf|5120078|F4321890CC18DD006D31BCDD9C9DBE5C|h=2PC3NLSYBRFDNZOSW73OBEQYSVWZPU7D|/