Home Site Map Links Wish List Search


I am no longer active in this hobby for the foreseeable future. 
I will no longer maintain or update the website, but I will leave it accessible to the web for as long as possible (years).


My Collection
Test Equipment
Model Rocketry

Bryan's Old Computers


The HP-01

The HP-01 is the only wristwatch ever made by Hewlett-Packard, and it was also an algebraic calculator. This was very unusual for 1977, but what makes this watch truly unusual, even today, is that HP integrated the time and date functions into the calculator! What this means is that the HP-01 can do time math, in real time! For example, enter in your hourly wage, multiply by time, and viola! Your earnings are displayed in real time, updated each second! This was touted as a tool for measuring the cost, in real time of such things as a long distance telephone call (always pricey in 1977). 

Another very cool function is the date calculator. With this, you can calculate days between dates, and even find the day of the week. The calendar is valid over 200 years, making this watch usable until the year 2100 without compensation. What fun...

The watch had at least a couple of bugs: One leap year date cannot be set directly. Y2K if I recall, although if set previously, the date would read correctly when it rolled around. The other is a divide by zero within a time calculation, as I recall. Don't do it! The watch will supposedly lock up (destructively?) until the batteries are removed! I have never verified either. I'm chicken.

If you would like more info on the HP-01, I know of no better source than The Museum of HP Calculators. I will not try to duplicate the information here. My page is a record of the restoration of two HP-01's; both a gold and a stainless steel version.

2008-05-06 Gold HP-01 015.jpg (1143715 bytes)
My gold HP-01, fully restored.

Both of my HP-01's were purchased though ebay. I paid too much for both of them, but they met my target price, and I knew I could restore them for less than the cost of buying one in better condition. The gold watch arrived in the most awful packaging I have ever seen, sparse toilet paper wrapping in a single box. Surprisingly, the watch was working and in pretty good physical condition other than a lot of small scratches. Fortunately, there were no problems with the glass. The stainless model arrived well packed, but in poor condition. The glass was chipped, and everything was well scratched and scraped; the stainless one had seen regular use over a long period of time. The stainless came with a case and accessories, and I was happy to get them, though I was disappointed with the overall condition.


HP-01 Restoration

Since I had never worked on an HP-01 before, the first part of this job was to figure out the disassembly. This got easier when I picked up a replacement battery pack with built-in cover remover! Getting beyond the back cover was a little more tricky though. Since I did not have the custom housing tools from HP, I had to improvise with a pair of  long needle nose pliers. I took an old pair, bent them and ground the tips down for a perfect fit.

Several notes of caution are in order here: This is a very old, very delicate, and expensive collectable watch. If you are not a skilled technician or at the very least, a skilled jeweler, don't do this! Also, work at a static free work station is mandatory!! (Skip this step at your own peril!) Also, the rear cover must be removed with a cover tool, NOT needle-nose pliers--damage to the piezoelectric buzzer can result, not to mention the pretty rear cover.

Finally, be very careful not to damage the water tight gaskets if you do not have replacements available! There are two of them, one just under the rear cover, the other between the two housing sections.

HP-01SS_0027.JPG (2901867 bytes)
Stainless steel model, all scratched up

2008-05-06a Gold HP-01 002a.jpg (706059 bytes)
Cover removal tool

2008-05-06a Gold HP-01 006a.jpg (1110400 bytes)

2008-05-06a Gold HP-01 011a.jpg (1856047 bytes)
Slotted rings & close-up

2008-05-06a Gold HP-01 015.jpg (2828478 bytes)
Inner ring removed

2008-05-06a Gold HP-01 016.jpg (3305262 bytes)
Split ring, in front housing

2008-05-06a Gold HP-01 018.jpg (3289943 bytes)
Close up of split ring

HP-01__0009.JPG (2903027 bytes)
Shiny parts, cleaned and polished.

hp-01_parts.jpg (2925071 bytes)
Watch bits, cleaned and polished


Ready? Here's how it goes: Remove the rear cover, batteries, and watch band. The watch band is fairly standard, but notice the small tabs at each corner. All of mine were bent out of shape--they are meant to lay flat against the bottom housing as can be seen in my 'cover' photo above.

Circled in the next photo, you can see two slotted rings under the rear cover. The inner ring is holding the plastic battery compartment tight in the housing, the other is holding the two halves of  housing together. Remove the inner ring by straddling the ends of the needle-nose pliers into slots on each side, and carefully turning counter-clockwise. Remove the plastic battery compartment. 

The remaining ring must then be loosened to allow the separation of the housing, and removal of the electronics. This ring is loosened using the needle-nose pliers in the same fashion, however, turn CLOCKWISE. The ring is held captive in the front housing, and after the housings are separated, removing this split ring to release the electronics can be done by raising one side, and then rotating the ring like unscrewing a light bulb. The raised end will rotate the ring right out of the housing. Easy, huh?

HP considered the electronics module to be a single, non-repairable item. If a watch was returned for warranty service, a faulty module was discarded and a new module inserted. This was the extent of repair available.

I have a different philosophy: Anything that ever worked can be made to work again, and anything that has ever been made can be made again. The only consideration is economy.

I suspect that most failures with the HP-01 electronics could be repaired economically today. This is based on my 25+ years of repairing somewhat similar items.  I would not consider die replacement economical, but many other failures could be undertaken with patience and a steady hand!

hp-01_hybrid.jpg (251783 bytes)
Hybrid module, lid-keypad removed, picture from HP

For example, in the hybrid photo, note the connector fingers along the right edge. The contacts are made between the modules halves with a 'zebra' strip, a flexible pad with many rows of conductors tightly spaced so as not to require a critical placement. The trouble with those things is that they can lose elasticity--breaking the intended connection, and may be a source of some module failures. Another possible--and potentially repairable source of failure is from circuit trace corrosion. This type of failure would result in 'open' connections where the original conductor has corroded away. This COULD be repairable by using a conductive silver epoxy or other conductive 'trace-on' circuit repair pen, if the damage is not too extensive and if the chips are not damaged. The hybrid appears to be hermetically sealed, if the seal is damaged, and the module is not working, this might be a hint of one of those 'uneconomical to repair' situations, but I would still not give up without a fight! :)
On the back side of the module, visible is the trimmer capacitor in the lower left corner. This is an easily replicable item, probably about 27pf. The crystal (cylinder in center of photo) is also easily replaced, and according to HP information, it is 38.4 KHz. Digikey is likely to carry this in stock for a dollar or two--though probably not in gold! The only other component visible here is the display current trimmer resistor of 330 ohms, 1/8 th watt. Ah, but the display!

OK, the display could pose a problem, but really, the only reasons imaginable for the display failure is physical damage or corrosion. It is possible that the solder connections could fail for a variety of reasons, but careful and skillful use of a good soldering iron can fix that. If the display is physically damaged, then repair could consist of trace repair with epoxy conductive glue, or replacement. I know of no source for replacement, but I would at least look before giving up.

Do you have a dead HP-01? Don't give up on it, it may yet be repairable!

HP-01SS_0003a.jpg (1036309 bytes)
Module back side, photographed on static-free mat, btw

Front Housing

After removing all front housing components, I used masking tape to protect everything  but the sides, which were to be buffed. The tape was pressed carefully all along the front keypad to keep the polishing process from touching.

Buffing was done on a 6 inch, 1/2 hp buffer, using red jewelers rouge to facilitate the buffing. A clean buff was done after the rouge, just to finish the job. This took patience, but removed nearly all scratches completely, as can be seen in the photo. If you have never done this before, I would advise practicing on something else first! Lots of practice!

2008-05-07 HP-01 002a.jpg (337101 bytes)
Side view of polished stainless steel front housing

Keys & Keyboard

The keyboard consists of small, round pins, with keyed placements to prevent rotation, and inserted from behind into holes in the front housing. These are held in place by a rubber water-proofing pad glued on the inner side. If needed, the lettering could be restored by steady hands and careful use of a Dremel with an extremely fine-tipped bit or sharp hand tools, but a laser would be best. This, with black, white, and yellow epoxy paint could yield very nice results. My gold watch required minimal repainting, and turned out quite nice as can be seen in the photos. The stainless model required no reconditioning of the keys. (I do not recommend removing the keys from the housing unless absolutely necessary.)

The key base, or background, is black with yellow lettering across the mid section. I cleaned the entire housing in soap and water, and dried with compressed air (Careful not to blow the rubber away from the key backing, or to blow the keys out of alignment! See photo below where the '9' key is rotated!). Next, I used a pre-paint cleaner to prep the surface for painting. For painting, I chose to use an airbrush with thicker paint than usual to lightly repaint the needed areas, hoping to fill scratches with the thicker paint. This worked well enough, I think. Finally, the sides were brush painted with black gloss two-part epoxy paint (acquired from a silk-screen printing outfit).

HP-01SS_0004a.jpg (1237582 bytes)
Stainless Steel model, as received


The glass on my stainless model was beyond saving. My only option was to live with chipped glass and a ruined silk-screen logo, or replace it with a new one. The search was on. I checked every source I could find for watch glass, and all to no avail.

My only chance was to re-invent the wheel, and have new glass custom made. I removed the existing glass and used it to reverse engineer a new one. After measuring and calculating all the angles, I created an exact duplicate in plastic and created a set of plans with silk-screen layout. The plans and duplicate were submitted to a manufacturing company, and as soon as I have trademark clearance, they are ready to go.

hp-01_crystal-front.jpg (82966 bytes)
Chipped crystal, removed from housing and cleaned

If I can get permission from HP to use the trademark, I will have a couple hundred of these made up and silk-screened, and will make them available here sometime in the near future. My estimate from the manufacturing company is nearly the same for a quantity order, so there is no sense in having just a few made. Do you need a new crystal? Contact me and I'll add your name to the list.

hp-01_dimentions.jpg (17207 bytes)
Housing dimensions

hp-01_dimentions_2.jpg (28434 bytes)
Glass dimensions & angles

hp-01_dimentions_3.jpg (16014 bytes)
Glass profile

Lower Housing & Band

The scratched lower housing and worn and scratched band required a lot of time and compromise to establish a workable restoration technique. The compromise was the loss of original material and thickness--only slightly, but when you are talking gold, anything is significant!

What I ended up doing was 'brushing' the metal with 120 grit sandpaper on a hobby belt sander. The results were fantastic, removing nearly all evidence of scratches and shine (where shine did not belong!), with a minimal loss of original material. It even worked well enough to remove the original owners engraving from the watch band! Sweet!

Before sanding the links, I used a hammer, small anvil, and a small, narrow, piece of flat steel to pound the 'C' shaped edge of the links to tighten them. Mine were very loose, and this worked very well to bring them back to original form and flexibility.


2008-05-07a_hp-01_001a.jpg (980318 bytes)
Brushing the band: rolling into the belt--downward in this photo (belt shown is not moving for the photo)

Also before sanding anything, I spent a lot of time practicing on stainless steel scrap, perfecting the technique to my satisfaction. Here is what I learned: run the belt sander at a medium speed, and at light pressure, 'roll' the work into the belt in the desired direction of the grain. Flat surfaces were held evenly against the belt all at once. The band links were not disassembled for this. Holding the band so as to roll it up in the hand, each link was sanded end-to-middle starting at the belt edge while rolling the hump of the link across the belt evenly at about two seconds per link, turning over to complete the entire link, and repeating as needed.


And now, for the pictures



HP-01SS_001.jpg (341616 bytes) HP-01SS_004.jpg (328108 bytes)
HP-01SS_005.jpg (425985 bytes) HP-01SS_006.jpg (393617 bytes)
HP-01SS_007.jpg (264499 bytes) HP-01SS_008.jpg (271931 bytes)




HP-01SS_010.jpg (497990 bytes) HP-01SS_011.jpg (475534 bytes)
HP-01SS_012.jpg (474383 bytes) HP-01SS_013.jpg (403171 bytes)
HP-01SS_014.jpg (457407 bytes) HP-01SS_015.jpg (463284 bytes)
HP-01SS_016.jpg (323004 bytes) HP-01SS_017.jpg (506382 bytes)
HP-01SS_018.jpg (426623 bytes) HP-01SS_019.jpg (420893 bytes)
HP-01SS_020.jpg (430453 bytes) HP-01__0014.JPG (2884917 bytes)




2008-05-06 Gold HP-01 011.jpg (1671133 bytes) 2008-05-06 Gold HP-01 015.jpg (1143715 bytes)

wordpress visitor

Unique Visitors Since 02/04

Copyright 2008 Bryan's Old Computers
Last modified:
October 16, 2009