Friden STW 10

The Friden calculators were very popular professional calculators in the US in the 1940's and 1950's. They were impressively large and fast, and built like tanks. The early ones like the 1941 Friden H8 (see video below) featured only additions and subtraction and were manually actuated. The later ones, like my 1956 STW 10, were electrically driven and feature multiplication and division. The last mechanical model, the SRW 10, even had a square root function! In 1962, Friden introduced one of the earliest transistorized electronic calculators, the EC-130 and then in 1964 the EC-132, also with a square root function.

The Friden company was founded in 1934 during the great depression by Swedish immigrant Carl Friden, and operated near San Francisco in San Leandro, California. It became the city's and one of the area largest employer. Unfortunately, after a long successful and inventive stretch under its visionary founder, it all went downhill when it was purchased in 1965 by the large German company Singer, which was unable to capitalize on Friden's early lead in electronic calculators.

I bought my Friden STW 10 on eBay and it arrived intact (a rare thing for such heavy items packed on the cheap by eBay sellers). Although it was in good shape cosmetically, it was in horrible shape mechanically. The restoration was very arduous, in part because I lacked documentation, and in other part because my machine was frozen solid, necessitating finding the faults one by one and unlocking things manually using a combination of cunning and forceful persuasion. See several videos below.

Friden Documentation

There was just about nothing available on the net when I tried to repair my Friden. But after the restoration, I found that a fellow still sold some copies of the old manuals. The copies were both expensive and of limited quality, but the that's all I have found. Unfortunately he has passed away, so you can't even "buy" the copies anymore. So I have taken the liberty to scan whatever I had, and post it below.

One of the most interesting document is the Friden W Line Mechanical Operations. This document tries to explain how everything works, and would have been invaluable if I had it during the restoration.

Next is the Service Manual, which is very hard to follow, has it only shows small portions of mechanisms you on many 100 pages, out of context. You have no idea where they are located in the machine, sometimes it took me hours to find it. They don't explain how it works, and the cryptic naming doesn't help either to figure out what function it does. But with some persistence I was eventually able to figure most of it out.

I wish I had the Disassembly Manual when I started, it would have saved me from a lot of trial and error, not to mention anguish when I first decided to remove the back plate.

The Friden STW Instruction Manual is the only original manual I own. It is a users' tutorial manual. I use this manual to follow the examples on my demonstration video.

Friden Calculator Demonstration Videos

This is a full demonstration of the repaired Friden STW 10. It's way more capable than you'd think. At the end I even calculate a square root.

This short one is one of my most popular videos. It shows a division by zero on the Friden, which produces intersting results.

The end of this video has great clip from the film "The Apartment", which shows a floor full of Fridens, typical of a large bank, accounting or insurance company installation.

Friden STW 10 Repair Videos

This is a full video of the restoration, from the start when it is completely frozen, to when I get it mostly working.

This video shows a follow up repair I had to do before it was filmed for a Japanese documentary. The documentary was about the contribution of NASA women engineers. Katherine Johnson famously used this very Friden model to compute orbits of the Mercury missions.

This video shows the repair and demo of an earlier manually operated Friden H8. I did as a summer intern project at the computer history museum.

Friden STW 10 Beauty Shot

The inside of the machine is spectacularly complicated, and photographer Kevin Twomey made a beautiful picture of the STW 10 innards after the restoration.

My Friden STW 10 photographed by Kevin Twomey