HP-01 The Hewlett-Packard Calculator Watch


Please help me!!!
I do own a HP-01 Calculator watch. The watch needs new batteries, but no watchmaker here in Germany is able to open the watch. Does someone know, where I can get a "battery replacement pack back"?!?
Greetings from Cologne



you could ask Matthias Wehrli (www.hp-collection.org) ;-)




The authentic case opening tool was part of the spare battery kit, which had three cells in a plastic container. Molded ridges on the container fit the notches in the HP-01 case back.

Someone was kind enough to machine a small piece of brass for me that fits two opposing notches.

However, more recently I saw that a friend had a generic jeweler's watch case tool, and I ordered one for myself. Here's the tool I purchased, though I ordered it from a different vendor:


All you have to do is use the three "slot" chucks, and adjust them to fit three out of the six slots of the HP-01 case back.



This tool is also available in Germany at http://www.reichelt.de/ order no. UWZ 083.



I hate to say this, but I think you need to find a better watchmaker :-)

AFAIK the HP01 back can be removed with a standard watch case opening tool, commonly (in the UK) called a 'JAXA tool' after the original (?) and IMHO best brand. This is an adjustable tool that has 3 interchangable tips (there are normally 4 sets of different tips with the tool), you select the tips that fit the slots in the watch back, put them into the tool, then adjust the tool so that the tips are the right spacing to fit the watch.

Be warned there are some clones of this tool around that are nowhere near as well made. A genuine JAXA tool will cost about \pounds 50.00 in the UK, if not more. Anything significantly cheaper is likely to be a copy.

And I am not rich enough to buy cheap tools (yes, there's a real JAXA in my toolkit...)


I've noticed that it's not as easy (or as cheap) to get batteries changed in watches. It used to be that every Jewelry store in the local malls would replace a watch battery - usually for just the cost of the battery or a flat $5 to $10 fee, including the battery. They would do this since they figured you would spend your waiting time looking at all the Jewelry in the cases and maybe they would make a sale to you. Most stores would also offer to clean your rings, etc. while you waited and hopefully shopped in the store.

A few years ago, I noticed that this started to change. Most stores would still replace the battery, but only on certain days - being when the store watch maker was on site. I'm guessing that too many watches were getting damaged by sales clerks who may not have been trained in the correct use of the tools.

When I tried to get some watch batteries changed earlier this year, I had a very difficult time finding any place that would do it. They all offered to send it back to the factory service center for a battery change - at a fairly hefty charge and waiting period. I ended up finding a retired watch repair person who replaced the batteries.

For the most part, these were just average watches - Seiko & Citizen. I expected to have problems finding someone to do my Wife's expensive watch, but it really supprised me with the plain Seiko which I've had for over 30 years.

Anyone else noticed this trend?



Bill --

I'm guessing that too many watches were getting damaged by sales clerks who may not have been trained in the correct use of the tools.

This happened once to the 1981 Seiko I still wear. The watch had to go back to the Seiko service center after a young clerk bent an internal part while installing the new cell. In recent years, I'd also taken it to a local watch repair shop that haven't done the job quite right, but at least didn't damage it. (The shop is no longer in business.) Having opened the back and done the job myself, I know how damage could happen.

In the 1990's, I always took the watch to an authorized Seiko repair shop 32 miles (50 km) away, run by an elderly man and his son. They always did the job right, for about $10.

When I tried to get some watch batteries changed earlier this year, I had a very difficult time finding any place that would do it. They all offered to send it back to the factory service center for a battery change - at a fairly hefty charge and waiting period. I ended up finding a retired watch repair person who replaced the batteries.

My most recent job was done by the Service Center, which did some other repair work. I wish that I'd obtained part numbers for the battery and gasket, so I can be fully prepared to do it myself.

Similar experiences!

-- KS


The last time I had someone else replace a watch battery, he picked up the new battery with metal tweezers, squeezed front-to-back (i.e., positive-to-negative, or a "short").

I don't know to what degree the battery life was shortened (pun intended), but I thought to myself, "I can do a better job than that!"

Edited: 18 July 2006, 2:29 p.m.


Tony wrote:

And I am not rich enough to buy cheap tools

I'm not rich enough to buy non-cheap tools for everything. I buy good tools where it's going to make a difference, and cheap tools where it won't. I spent $20 on the clone of the Bergeon JAXA tool, and it works fine for opening my HP-01 once or twice a year. If I had to open watches several times a week, I'd consider spending $100 to get the real thing. On the other hand, though, I'd also consider that there doesn't actually seem to be anything wrong with the $20 tool, so I wouldn't be eager to spend that $100 until I was convinced that it actually would be noticably better.

The tools that I use most are my PC, and especially its human-interface devices: monitor, keyboard, and mouse. I bought the best I could afford. For example, the monitor is a Samsung SyncMaster 213T 21" LCD (1600x1200), and the keyboard is a Northgate Omnikey Ultra T. If I had to buy another keyboard, I'd probably either get a refurbished Omnikey, an EnduraPro from pckeyboard.com, or a Das Keyboard II. Hmmm... maybe I'll buy an extra Omnikey Ultra T just in case.

Note that "the best I can afford" is most often NOT the same thing as "the most expensive I can afford".

I have a Hakko soldering station which is reasonably good, but at some point I think I'll buy a Metcal.

I needed a hammer-drill for a single use, and rather than spend $150 for a good quality name brand one, I spent $15 plus $5 postage for an inexpensive Chinese one. I expected that it would work at least well enough for the single use, and then I could throw it away if it didn't seem like a good tool. As it turned out, it worked perfectly and I expect that if I ever need it again, it will be fine.


I bought my watch tool on sale at Harbor Freight for $5 (usually $8-10). Made in India. Has actually done the job very well every time I needed it to. Sometimes a cheap tool is all it takes.


I couldn't agree more with this aphorism.

Many a time I was tempted to buy a cheap tool, and in cases where I gave in to this temptation, I was sorely disappointed.

Consider a drill stand, I was only going to use it once for one job so I bought a cheap chinese one. It worked all right, so I kept it, and when I needed to use it again I brought it out and went to work. It broke half way through the job (unbelievable, its a metal construction and the crack appeared in the movable part holding the drill). Now I had to buy another stand to finish the job, but I was also in the middle of the job with everything taken apart and I was in Greece at the time where there are no 24 hour Home Depot stores :-(

Screwdriver kits are the next best example, where you get huge collections of single use tools. After some time you have piles of the parts that you do not use often, while the ones you do use are useless.



Whether or not I buy good or cheap tools does not depend on how often I use it rather it depends on how critical the task is. I think opening an HP-01 back is critical enough to get the best tool available. Low quality tool may damage the watch even if you use it only once.


But inexpensive and low quality aren't necessarily correlated. The inexpensive tool probably isn't quite as good as the JAXA tool Tony mentioned, but there doesn't seem to be anything at all wrong with it. There's no obvious way that you could damage the HP-01 with it when using it properly.

The only obvious failure modes would be for one of the bits to break, or for one of the chuck adjustments to come loose. Neither is very likely. Either occurrence won't scratch or damage the watch unless you're applying excessive force or nor holding the watch firmly.

I agree that I wouldn't use a tool known to be of poor quality.


OK; i'm going way off topic here but does anyone else use Plomb (not f'in plumb) mechanic's tools? They are way too large to use on our little hp jewels but they are fine. I inherited most of my set from my dad who bought them when he got home from his South Pacific vacation in 1945. The newest was made in 1947 and they have been in use since then. That's good steel.


The clone JAXA tool that I saw had a lot more sideways play in the adjustable chucks (that is, they were loose in the frames) than the real one.

My worry would be that that would allow the tool bits to slip out of the notches in the HP01 (or other watch) back, and put a nasty scratch on the latter.

Maybe I am just overcautious (or maybe I was just lucky to find a real JAXA tool for less than the cost of most clones!).

As regards another comment about cheap sets of tools (screwdrivers with interchangeable bits, etc), one criterion I put on buying a set of tools is that all the parts are available separately (they are for most good-quality sets). That way, if I damage one, or lose one, or need an extra (e.g. to have 2 sockets of the same size, one for the nut, the other for the botl head), I can get it.

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