HP 42s -- "TOP.FCN"


Hi, everyone, I'm doing a school research about several calculators (I chose the HP Pioneer series calculators), and I came across an interesting aspect concerning HP 42s. I don't own one myself, and since I don't have access to a manual, I am not really sure; but my question is what is the purpose of the "TOP.FCN" menu accessed above the zero key? I found out that by activating that menu, one would simply get a menu with items corresponding to the functions on the top row of the calculator: sigma plus, reciprocal, square root, logarithm, natural logarithm, and execute. Isn't it kind of weird? One could just press the physical square root key, for instance, to find the square root of a number; it would be a waste of two keystrokes to access the TOP.FCN menu just to accomplish what could easily be done with one key press. Please help me out, I'm not too knowledgeable (yet) and it's just killing me not knowing the exact purpose of the TOP.FCN menu of the HP 42s, because right now to me, it seems redundant and a waste of menu/function/space. Thank you. :)


If you have another menu currently in use, and you want to use one of the normal top row functions (e.g., 1/x) the TOP.FCN key temporarily brings up their functionality. Once the button has been pressed, the menu returns to the previously displayed menu.

This is from memory - am I right?

Nigel (UK)



I have just tried what you mentioned. It does not seem to work.

I used the HP42 regularly back in the early 90s, but I cannot remember ever using TOP.FCN.

The manual clearly backs you up. A possible bug?


I don't have a physical 42s anymore, but I do recall this is the correct use and behaviour of the TOP.FCN key. Also, Free42 on my N900 works like this as well.


I concur with Stuart. Neither my 42S nor Free42 returns to the menu displayed before TOP.FCN. For reproducibility tests, what I did is:

gold FLAGS    displays the flags menu
gold TOP.FCN displays the menu of unshifted top functions
SQRT 3rd menu key executes the square root
and returns to 2-line display of x and y
No manual at hand right now.


OK, found it on pp. 22 and 23 of the manual:

Pressing TOP.FCN (top-row functions) displays
a menu containing the functions (shifted and unshifted) on the
six top-row keys: ... Use the TOP.FCN menu when you want to use one of these functions without exiting from the current application menu.

Emphasis added. In the 42S, there are two kinds of menus. You have to know by heart which's which, you can't see it on the calc :(


Some of the menus are "passive" and would normally disappear after one of the choices is taken. Even when you temporarily "lock those in" by "double-clutching" into them, they disappear after a completed TOP.FCN.

However, the "active" menus (SOLVER, BASE, etc.) which "stick around" until explicitly "EXITed-out-of" will resume where you left off after a TOP.FCN task.

I didn't try anything with a programmed set of menu variables in action, so am not sure which side of the ditch that tree would fall.


Maybe I should have been more precise. For sake of unambiguity, here's what they wrote on top of p.22 about it:

Nothing about "active" or "passive" ... but you have to learn the five "application menus" :-( And please don't ask me why it was structured this way - it's the way it is :-/

Edited: 8 Mar 2011, 4:14 p.m.


The general idea is that "application" menus are menus that you'll spend a lot of time with, and will want to return to after using some other menus for some quick calculations.

The application menus on the keyboard are SOLVER, the integrator, MATRIX, STAT, and BASE. The variables menu (VARMENU) also acts like an application menu.

So, you can go to MATRIX and then EDIT or EDITN, and while editing a matrix element, use menus like PROB or PRINT without losing your place in the matrix editor. The TOP.FCN menu lets you access the normal functions on the top row of the keyboard, again without having to back all the way out of the MATRIX menu (the MATRIX "application", per the manual).

The HP-42S menu system is quite clever; it's designed to minimize the number of times you have to deliberately tell it to switch menus. The HP-42S manual explains it all quite well... If only HP had released that manual into the public domain! *sigh*



I urge you to install the very nice Free42 by Thomas Okken. It is just great.





While you're there and since you don't have a manual you can download the "Alternative HP-42S/Free42 Manual", written by José Lauro Strapasson and Russ Jones from Thomas's site as well.


Thank you all for your responses. :) Thank you Mr. Rasmussen for the link to the Free 42s, that is pretty neat! I'll download it later when I get a chance today. And thank you Mr. Walter B. for the manual excerpt, really helps. Though I still wonder because, let's say that we have the CATALOG menu activated, then let's say we want to take the square root of a number. We could do two things: (a) activate the TOP.FCN menu by pressing the SHIFT key then the zero key, for a total of two key presses, or we could (b) just press EXIT, for a total of one key press. And wouldn't one not return back to the CATALOG menu after taking the square root of a number using method (a), hypothetically in our example, but return instead to the regular X-Y display (not back to the screen with the CATALOG menu still activated)? I may be being a little too discerning, but I'm just wondering. :)

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