How to open the 30 series calculator (HP37E) - Hidden screw?


Hi fellow HP enthusiasts,

Today while at a yard sale I found another member for my HP calculator collection. It is a HP37E and it will be my third calculator. It has a bad battery (of course), with just a little hint of corrosion on the contacts, plus one of the contacts was broken off but was still inside the calculator, so I managed to reattach it with a bit of solder. Also the two rubber feet on the battery cover seem to be crumbling away (heat from the batteries?). The other two feet look fine. The only accessory was the soft carry case in very good shape, but no charger, and no manual. Already tested the calculator and it's working perfectly, and all keys work nicely, feel like new. Just needs a bit of overall TLC. Price: $4.

In order to clean it properly, I was trying to open the HP37E and removed the two screws that become visible once one takes off the battery cover. After that I tried to open both halves of the body but there seems to be something else holding the shells together on the other end, like a hidden screw somewhere in the area of the "Hewlett Packard 37E" label that is just bellow the keyboard (feels like it is somewhere between the "0" and the "." keys). I checked under the rubber feet, but nothing there. Don't see any other obvious area where hidden screws could be.

Could somebody please let me know what am I missing. Thanks.


Caracas, Venezuela

PS. My other two calculators are a HP45 in it's original hard case, charger, soft case, quick reference manual (no user manual), and the blue envelope with "Important Warranty Information Inside". The other is a HP41C in original cardboard box, with all the original manuals and standard accessories. Also a few weeks ago I found a HP35 hard case, but could not find anything else related to the calculator. Price of that one: free.

Edited: 9 May 2005, 9:22 a.m. after one or more responses were posted


Hola, Alex; como estás?

I think the drawing below (a cut, calculator upside down) will help you figuring out a way to "unlock" it:

There are many technics explored by some brainy contributors in here. I'm not completely sure if there are descriptions on how to open a Spice at the Articles Forum, but it's worth checking it out:

One I like most, although I never tried it yet, uses dental floss (to the contributor that created this method: please, forgive me: I forgot who's the one!). It does not allow the external thin plastic tab, that ensures the locker is kept, to break when opening the calculator.

Hope you succeed!

Luiz (Brazil)

Edited: 30 Apr 2005, 10:57 p.m.


Hola Luis,

Thanks for taking the time to respond to my post. Your drawing made it clear to me how the bottom half of the case is held together, but I just now tried again to separate it but was not successful. After opening it, I pushed the rear shell down a bit to try and disengage the lock, also tried to wiggle it a bit, but no luck so far. Wish I knew for sure what the correct opening technique is before starting to try again. There seems quite a bit of resistance to separate both halves of the case.

Can anybody tell me if I'm just supposed to pull both halves apart until the lock lets go? Looks like it could snap, and I really would hate to break something just by applying excessive force.

Thanks again.


Edited: 1 May 2005, 1:10 a.m.


Have a look at Tony's suggestions



Hi, Massimo! Are you well?

I lost your e-mail! Can you help me to 'update' my 'friendship database'? Please, drop me some lines...

lcvieira at quantica dot com dot br

Best regards.

Luiz (Brazil)

123456 to remove


Hi Luiz... you have mail!

Oh, BTW, here is the relevant link Tony pointed to:



Hey guys,

I just went to Tony's website and definitively a picture is worth a thousand words!! I just used the "special grip" and it opened in a heartbeat without much fuss. It just clicked and easily came apart.

Thanks Luis and Massimo (and Tony).



It's not my site. It's Hugh's (another HPCC member).


OK I'm now taking the calculator front case to the sink for a quick and gentle wash. I like to use a soft worn tooth brush and some mild hand soap to clean the front panel and the keys. gets off all the gunk and dirt without harming the lettering.

One question: what is the function of the BEGIN/END switch? I don't have the manual so no idea. First time I see this on a HP calculator.

And while were at this topic, anybody knows where I could download a user manual for this model?




Hi, Alex;

as you can see, the HP37E is a financial-oriented calculator. When you are dealing with compound interest investments, meaning accrued interest for each period, one can choose payment (periodic investment, if applicable) either in the BEGinning or in the END of each period.

You can use the HP12C manuals as a reference for that, and you can download any of them for free here.

The HP37E is sort of a low-budget financial calculator. Compared to the HP12C (or its 'related' partner, the HP38E) it has no discounted cash flow features, no programmability and no ability to deal with dates (neither with bonds nor depreciation). It is also one of the fewest RPN HP calculators without LASTx. It is a real collector's choice...

I have the original HP37E Owner's Manual, but it is a Portuguese printing. For me it's fine, but...

If you have other questions, post again. BTW, I do the same as you're doing: dismantle the calculators and wash them. I just use a few drops of neutral liquid soap (detergent) with water to wash the case and keys.

Success with your new(old?) financial calculator.

Best regards

Luiz (Brazil)

Edited: 1 May 2005, 7:01 p.m.


Hi Luis,

Yes I was looking for the manual because I'm not sure how the financial functions are used. The arithmetic and scientific ones I have no problems with.

I just finished putting the calculator back together a while ago. Looks nice, almost as new. While it's apart, I also clean the contacts and pads of the slide switches with absolute alcohol, that removes some grime and old dried out lubricants, and then apply a little bit of special Teflon grease. That insures long life and minimum wear on the contacts. These where almost new, I think this calculator saw very little use.

I like to use hand soap to wash the case shells and buttons because it is very mild and will not react on the lettering of the equipment, and gets the cleaning job done very nicely. I usually give any used equipment I buy the same treatment. BTW I also collect Heathkit gear, especially test equipment because I usually end up using it (have an electronics hobby bench at home), and not just putting it on the shelf to admire. Same with the calculators, they are all side by side on my desk, and nowadays I mostly use the HP41C, but from time to time, and before getting the 41, I always used the HP45. I also like to restore tube audio gear and I'm presently working on my first project, a Fisher X-202-B integrated amplifier.

Just downloaded the HP12C manual, will study it to get familiar with the financial functions. It's really more out of curiosity than need, but one never knows when some of those functions could come in handy.

Thanks for all your help, and the offer of a copy of your HP37E Portuguese manual. You're right, unfortunately it won't do me much good.

Good luck.


Edited: 1 May 2005, 9:44 p.m.


Hi, Alex;

good to know about your electronics acquaintance. I also have a workbench at home, not all equipment I'd like to, but somehow it fits my primary needs.

About Fisher: I remember seeing many Fisher audio equipment in old catalogs. I also remember that they were beautiful pieces, with wood ends at both left and right sides, and 'fancy' front panels. I'd just like to know if the one you mention, the X-202-B integrated amplifier is one of these. You see, I still like home electronic devices (audio & video) that actually mix with the furniture. A few days ago I bought an Akai 4000DS, a tape recorder. After disassembling and cleaning all of the front-panel parts, it was enough to replace two rectifiers (mains supply) and the AC fuse to bring it back to life. I even painted some parts in flat black. Now it is cosmetic and electronically good enough to play tapes. You see, I don't like too much those 'sci-fi' like equipment that actually do the same as the old ones. And also do not last longer...

As this is a calculator-related site, if you feel comfortable e-mailing me about the subject, please, be my guest.

lcvieira at quantica dot com dot br


Luiz (Brazil)

123456 to remove


OK Luis, I will email you tomorrow evening with a little more time. I have an early day tomorrow, so I'll be excusing myself for now.



... to use a thin, flexible plastic sheet, something like a telephone or credit card, the thinner you find, and try to gently insert it between the half cases, in the corner, while wiggling the lower case. If you succeed, the thin plastic should help the half cases sliding over each other. And the separation leads to a noisy 'snap' sound; sometimes it seems something has broken, but it doesn't mean it did! ;-)

Also, please take Massimo's warning and read Tony's post. Very good warnings there!


Luiz (Brazil)

Edited: 1 May 2005, 1:17 p.m.

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