Dating slide rules

Recent Posts
  1. My Slide Rule Collection
  2. SRTC: Hemmi Catalogue Raisonne: Estimating Dates
  3. Slide rule
  4. Navigation menu
  5. Navigation

We know of no other H-suffix Post slide rules.

My Slide Rule Collection

For example, in the Post catalog, , A, B, and C indicated different models of Richardson slide rules. These were catalog numbers, not model numbers; we don't believe that these numbers actually appeared on the rules. Teledyne continued the old numbering system for a few years after it took over Post in but, about , Teledyne Post introduced the ' 44 ' numbering system. In this system, the last place in the catalog number indicated various combinations of case, instructions, and display boxes.

For example, the Teledyne Post model number for the 5-inch pocket Versalog was 44DA, but, when sold with an instruction manual, the catalog number was 44DAL; and when sold without the instruction manual, the catalog number was 44DAO letter 'O'. The Table of Post Slide Rules.

We have listed, in the accompanying table, every slide rule sold by Post or Teledyne Post for which we can establish a catalog number. Listing all slide rules ever sold by Post is an impossible goal; Post sold many special-purpose rules that were not listed in its catalogs. To quote the Frederick Post Catalog: Many Post catalog numbers were duplicated over the years, with being the most popular. There are 16 different rules bearing the number , including suffixes, from to Some are variants within the model number series, and some are completely different rules.

The series also has several variants. The Versalog itself shares its catalog number with two other, totally different, rules, the Ritow High School Mannheim inch rule from the catalog, and the Engineer's Universal Duplex inch rule from the catalog. The inch model , listed in the catalog, has likewise caused considerable confusion with the popular 5-inch pocket Versalog model The table gives the catalog number and characteristics of each rule.

Important variants of each slide rule are listed separately.

SRTC: Hemmi Catalogue Raisonne: Estimating Dates

We considered the following factors to be important enough to warrant listing slide rules as separate variations:. Nevertheless we have listed these as separate variants because the Versalog is so popular among collectors. And, besides, we can violate our own rules if we want. We owe particular thanks to the many slide rule collectors who shared information with us. This article is based on our own collections of Post slide rules, Frederick Post catalogs and price lists, various instruction manuals and other documents, and information from other collectors.

We believe our statements to be accurate, but much of our knowledge rests upon weak or ambiguous evidence so there are surely quite a few errors. We shall be indebted to anyone who can supply corrections or new information. Please address correspondence to Ted Hume, P. Everything from Quotes and SciFi to Ethics. Sphere Research Corporation Sunnyside Rd. May June July Aug. Click for bigger PIC! You are visitor number. This Archive is the result of 2 years of extensive research and investigation by Paul Ross and Ted Hume, who have kindly allowed us to publish the results of their work here.

To contact the project researchers, see the data below: Paul Ross 52 Sheridan Rd.

Slide rule

Or wood, with celluloid laminate on top. And the cursors were typically made out of aluminum or steel or brass, tin-plated, and glass or plastic lenses with one or more hairlines, depending on the type of slide rule. Some of the cheaper slide rules were just a piece of wood with the scales printed on it. At one time you could buy a low-end slide rule for a quarter. And I remember as a kid at 13 years old, I had gone to the National Association of Rocketry, and we used slide rules to determine how high our rockets went.

And you could get a cheap slide rule through the folks that sold the rocket motors. Another difference between slide rules was how they did the division markers. The earlier slide rules were all done by hand. They had a master, and the guy would just sit there and cut the grooves and hand-engrave the numbers in. Later on, they were mass produced, and manufacturers competed to see how many scales they could get onto a slide rule scales were equivalent to the buttons on your calculator. For many years, most only had six or seven scales. But then the geeks in the schools, of which I was one, would want slide rules that had more and more scales on them.

You could do any math problem you wanted on your basic slide rule, but the ones with more scales saved you steps. William Oughtred is credited as the inventor of the slide rule. He basically took two logarithmic scales and put them next to each other and figured out that you could multiply and divide by adding the logarithms together. He lived from to The earlier models were all made out of wood. Then around , they started putting white celluloid on top of the wood.

The celluloid starts to yellow and gets that patina. The laminated slide rules made for a better contrast and made it easier to clean.

It also kept them from warping. Two of the biggest slide rules makers in America were Pickett and Keuffel and Esser. Pickett started making them out of magnesium at the end of World War II and then switched to aluminum. They had some corrosion problems. Keuffel and Esser, they used mahogany on theirs with plastic laminate later on. Around there was Gilson.

And Dietzgen was another big American one.

Post sold a lot of slide rules under the name of Frederick Post, and later on just Post, which later became Teledyne. I personally tend to like the earlier American manufacturers like George Richardson. He made the slide rules in his home and shipped them out to folks. When he sold out, it was to another family, and they did the same. The other majors were named after their founders as well.

Pickett was named after Don Pickett. They sold drafting supplies and other tools as well. Some manufacturers just made slide rules, but others made drafting instruments and anything that had scales on it or was used for mechanical drawing. I was a product of the whole generation of engineers who started with drafting boards and slide rules and ending up with electronic calculators and computers.

Navigation menu

Lawrence made the low-end slide rules, and they later became Sterling and spun off a few other makers. Acu-Math was another big one. After World War II when we were trying to help the Japanese get back into business, we would import a lot of Japanese slide rules and with different American brands on them. So they all looked the same except for the logo of whatever company was distributing them. In fact, there was a big business just selling slide rules to U. To companies like JC Penney and Sears, who offered them in every catalog. They were just re-branding them. In Europe, two big manufacturers were Faber-Castell originally A.

Faber and Aristo, both out of Germany. William Oughtred was an Anglican priest in England. And there were others — Unique at the low end, Sperry, Polar and so on. The scales were the same. The metric system was used in all the slide rules, so it was really a matter of how many different colored inks you might use or the size or the placement of the slide rule.

The scales were basically either 10 centimeters or 10 inches. If they had a inch scale, all the divisions were based on that overall length. And so the sizes they had were the 5-inch long pocket slide rule, the inch standard slide rule, and the inch long, which gave you a little bit more accuracy when you were trying to extrapolate. They also had these really large teaching and demonstration slide rules.

Pickett actually gave these out free to any school that ordered 20 slide rules, to hang on the wall. Once you chose your slide rule manufacturer as a student, you had a tendency to stay with that manufacturer as you went through life. So it was marketing. Most slide rules sold in other countries either came in cardboard or plastic cases, so this was a new requirement. It was just our standard of quality that we wanted to have. There were also circular slide rules.

You still have the same resolution with the scales as you would on a larger slide rule. So circular slide rules were really good for increasing the space between the divisions to get more decimal points, or to be able to extrapolate where you thought the scales would be or the number that you were looking for. The s, especially during and after World War II.

Slide rules were put on every airplane to calculate mileage for navigation. Thousands of slide rules were used on Navy ships for maritime navigation.


As we became more and more industrialized, every engineer had slide rules and every math student used them. As people became more and more educated, slide rules were used more and more. And the slide rules that John Glen used when he went up in space. They took slide rules on the Apollo mission to the moon. They were just a part of our work. It was something everybody had. It was something that helped you compute some conversion for a specific job.

They actually called it the slide rule calculator or even the electronic slide rule Texas Instruments called one model that. Every engineering student immediately wanted to buy one, although they cost a lot of money. But even slide rules, the top of the line, most advanced ones, were pretty expensive back then. But everybody had to have one for school. By the end of the s, all the slide rule manufacturers died. Pickett went out of business, and sent all their slide rules out to be scrapped somebody else retrieved them and stored them for the next 27 years.

The companies that relied on selling slide rules disappeared altogether. Those that could move into the computer age did so, but there were a lot of fortunes lost. Teledyne had bought Post in the late s, and then within two years no one was buying slide rules anymore. Some of them tried making electronic calculators too. They had a cost advantage. Interestingly, the first calculators that came out only did basic math, but not yet any of the scientific or trig functions like sine, cosine, tangent and inverse sine and square roots.

So there were several models sold that had a math calculator on one side and a slide rule glued to the back to do those other functions. The disappearance of the slide rule is disappointing because when you used a slide rule, you never knew where to put the decimal point. You had to extrapolate in your head. The calculator does, and it gives you the answer up to eight decimal places, which hardly anybody really needs.

Some collect technical instruments like pantographs. But many slide rule collectors just focus on trying to collect every type of slide rule they possibly can. It was a piece of art. Unfortunately a lot of the guys who are interested in slide rules are fairly old, generally 50s and above. Hemmi referred to it as the "Type B" cursor. It first appeared in the Hemmi catalog and had vanished from Hemmi material by A magnifying version was available. Cursor C is Hemmi's famous "Type A"--patent cursor.

Construction is polished aluminum. An interesting variant of the type A cursor is the "extended magnifying lens" cursor from None is known to have survived. This improved type A cursor was introduced about on Hemmi's less sophisticated rules and gradually supplanted the type A cursor on other rules, completely replacing it around WWII. Hemmi re-introduced all-plastic cursors on its less sophisticated rules in the s. There is a wide variety, ranging from small cursors with high magnification to elaborate, multi-line cursors.

These cursors are too varied to be described by any general principles but their slide rules usually carry date codes. All Hemmi five -inch bamboo duplex rules use chrome-framed glass cursors like this. Hemmi plastic duplex slide rules used all-plastic cursors like those shown in the illustration at right. The design on the left was used on extra-thick about 5mm duplex rules. The design on the right was used on thinner 4mm rules. I have not been able to narrow the date. Rules with model numbers date from before this changeover, rules with model numbers 20 and above were made after the changeover.

Hemmi continued offering models 1, 5 and 8 to its distributors until WWII or later; these rules occasionally turn up with Post or Hughes-Owens model numbers but no Hemmi model number. The company name was officially changed from "J. Hemmi was incorporated as a public corporation with no change in name. The first inch or first five centimeters of the measuring scales on ten-inch closed body rules is extra-finely divided. Note the S scale on the upper slide in the illustration. The S scale on the lower slide in the illustration is an example.

Both slides are from Hemmi model 50W slide rules; the upper from a rule dated September ; the lower from a 50W dated May That can make it difficult to find. It sometimes takes inspection with a magnifier in raking light to find the code. The date codes reveal the date of most post Hemmi slide rules but it is not absolutely reliable. A very few have two different date code.