Refurbish an Old Slide Rule

Some guys my age buy the nice car they never had in high school.  I went on eBay and bought the nice slide rule I never had in high school.  It cost far less than the car!  (The photo are from Slide Rule Museum and Bing Images.)

Step 1 What to pay

I went on eBay and bought a Dietzgen Polymath #1733 Decimal Trig Log Log slide rule from the mid-1950s for $2.50 (plus $9.50 for shipping).  If you were at the US Naval Academy in Annapolis, MD; this slide rule was standard issue for plebes in 1955.  These can go for between $40 US used and $500 US for one never sold still in the original box with the original manual.  I was the only bidder, probably because one of the cursor glasses is missing and the other is broken.  In the photo you can see the line from the break. Otherwise, this slide rule is in quite good condition.  It shows no discoloration anywhere.  There are a few light surface scratches from normal use.  Neither the wood from which it is made, nor the plastic laminated to it are cracked or broken in any way.  The slider action is smooth.  It does have someone's initials scratched into one end of the slider.  The original leather case is even in quite good condition.  I will show several things in this Instructable, including how to make new cursor glass from Plexiglass and how to inscribe it with a very fine cursor line, also known as a hairline.

Comments

[old_code]

I miss my slide rules, long packed away for safety and replaced by darned calculators. I was fortunate to have used slide rules for 3 or 4 years in high school before calculators were slowly being allowed (only the most basic ones were allowed to be used for tests, but you could use a "scientific" in class. Mine was a TI SR-50, also stored away.)

You've written an incredible 'ible, with great pictures and thorough explanations. And an abundance of reference links. Your passion for this piece of work has stood out.

Thanks. Good to see passion in this world; too often the bland and brainless of the TV and iPod generation predominates.

[Phil B]

Thank you for your comment. I missed it until now. I do enjoy my "new" slide rule as much as I would have enjoyed a red sports car, and it cost a whole lot less. Plus, I like to say that when I am out around town playing with my slide rule, my wife does not need to worry about me bringing home any strange women.

[dps john]

There used to be an old joke that if you asked a guy who worked in a drawing office what 2 x 2 was he would take a 6 inch slide rule out of his top pocket fiddle with it and say about 4.
The older slide rules were made of wood with a type of plastic plastic face (Some of the very old ones had a horn facing) and were engine devided

[Phil B]

It is probably true that engineering types would consult their slide rules for a problem like 2 x 2 and then say the answer is "about 4." I heard an old story that a reporter had interviewed Einstein. At the end of the interview the reporter asked Einstein what the speed of light is. Einstein reached for a reference book. The astounded reporter said, "Dr. Einstein, you do not know the speed of light?" Einstein said, "I never clutter my mind with things I can find in a reference book."

The lines on my new old Dietzgen are very precise and very nice. It seems like a lot of work, machine engine or not, to cut each line into the celluloid. Pickett printed most of their rules on aluminum, at least since the 1930s. Some were printed on plastic, but mostly for students. Mahogany and bamboo seem to hold up well for making slide rules. Interestingly, the recommended technique for cleaning up the surface of a rule made from wood covered with celluloid is to rub out small scratches with a fine steel wool. I cannot quite bring myself to do that.

There are photos from the early days of computers. Offices would have a slide rule mounted on the wall in a shadow box. Underneath was a sign that said, "In case of emergency, break glass."

Thank you for your comment.

[rimar2000]

These little devices are awesome. When I studied astronomy, between 1962 and 1965, came to dominate them to quickly execute a number of quite complicated calculations. Obviously, today they are museum pieces, because electronic calculators outscored them absolutely.

[Phil B]

Osvaldo, someone called slide rules "the original pocket calculator." And, you never need to worry about needing new batteries or having enough sunlight for the solar cell to provide enough power! I have been reading on-line articles about them. Apparently some people still prefer them to electronic calculators and use them for real mathematical calculations. Slide rules force the user to understand the calculation and to be more involved in it than does a calculator. There are always a large number of slide rules for sale on auction sites like eBay. Many who buy them are collectors, although some buy them for nostalgia. But, eBay slide rules sometimes have a bad reputation because of missing pieces or being in worse condition than the seller described. My goal with this Instructable is to show there are ways a buyer can restore a slide rule, himself. That means a buyer can buy a functional slide rule for a low price and make it work again for very little money. The alternative is to pay a lot of money for a pristine slide rule on a site that sells rules in nearly new condition. Some calculations are actually faster on a slide rule than on a calculator. For example if I need to know what 1 divided by 5.3 is, I can simply move the cursor to 5.3 on C or D and read the answer directly on C1 or D1 without even moving the slider. As I work through the manual for my slide rule I often find my answers vary slightly from the answer given for the practice exercises, but my answers are within about one tenth of one percent of the answer listed. That is the expected range of error for a ten inch (25 centimeter) rule.

[rimar2000]

Yes, they are ideal for phisic calculations, where isn't needed absolute precision. In my case, I used them for astronomy, where generally there are two or three digits and a "magnitude order". When the user learn to use them, they are very very speedy. But they aren't suitable for countable calcs, when mainly one must do additions and substractions, and the precision is very important.

[gandlof5]

The one other thing about using a slide rule is you have to know scientific notation, and how to treat numbers exprested as such in differnt operations. Now kids ask what do I need that for?

[Phil B]

When I was a kid I also questioned the value of many things I later learned I did, in fact, need to know and use. You have probably found scientific notation is helpful when you want to do a calculation with numbers so large that they are beyond the range of your electronic calculator. Scientific notation is helpful when using a slide rule, even essential for some calculations; but many slide rule calculations can be approximated quite successfully for the purpose of knowing where to place the decimal point. For example, 3.85 x 4812 can be severely rounded off to 4 x 5000 so the user knows the problem will have an answer within range of 20,000.

[PurplePeople]

Kudos! This is quite a good tutorial. I have a small collection myself and keep a number of 6" rules for everyday use.

[Phil B]

Thank you. I still have a Pickett 120 Trainer I bought about 1960 early in my high school years. In college I bought a cheap 6 inch plastic rule at a five and dime store so I could carry it in my shirt pocket. I wanted it so I could quickly calculate the price per ounce for comparison shopping. Now those figures are often on the price label. About 1970 I found a nice PIckett log log 5 inch (6 inch?) aluminum slide rule that fell out of someone's pocket onto a street. The owner had carried it in his hip pocket and the rule was bent a little. I did not use it much, so I gave it away a few years later.

[kill-a-watt]

Hah, I need to shop where you shop. Here they have the unit price, but they play games with the units. For instance, they price the deli meat in $ per Lb. but price the packaged lunch meat as $ per ounce. If you do the math yourself you'll see they're asking $3 per pound for slices of whipped fat.

That and the fact that the unit price is frequently dead wrong. I keep a calculator handy and also have a $/oz to $/lb "cheat sheet" handy in my PDA

I've always wanted to learn the slipstick, but couldn't ever "get it" using the online simulations. I remember playing "lunar lander" on my dad's first programmable calculator, if that dates me.

[Phil B]

I remember when I was eager to have a digital watch with a calculator built into it just so I would always have a calculator with me. Now calculators are built into everything, even the cell phones most of us carry at all times. I remember one high school teacher explaining basic slide rule functions to us with one of those demonstration rules about four feet long that hung at the front of the room. But, I had already bought my Pickett 120 and taught myself the most used functions. The PIckett 120 manual was basic, but pretty easy to follow. That manual is available on-line here.  (Search the page for "120" or look for M52.)  Before I found the Dietzgen manuals on-line, I downloaded a manual for a some other log log rule. The Dietzgen manual is much better written and easier to follow. Even if I become a little confused by the verbiage, doing the sample problems usually makes it clear. I would encourage you to proceed and learn to use a slide rule. You may not need to learn to use a slide rule, but it will give you a feeling of accomplishment. In my opinion, one of the most important parts of learning is practice reading numbers on the scales accurately and as fast as is practical.  With the virtual slide rule I linked you do not even need to buy your own slide rule.

[NachoMahma]

.  Great job. I only used a slip stick for a few years before hand-held digital calculators were introduced (somewhere around 1972, IIRC). I may have to look through some boxes and see if I can find one of my old 'rules.

.  I would swap the intro pic so a sliderule shows up in the listings. Great looking car, but it doesn't have much to do with sliderules.

[Phil B]

You make a good point about the car in the introductory photo. I was attracted to using it because of the contrast between spending thousands on a nostalgia car versus spending lunch money on a nice slide rule. I thought it might serve to pique the interest of viewers who wonder what a nice car has in connection with a slide rule. I value your reaction and will give it serious consideration.

The Hewlett-Packard HP35 electronic calculator appeared in 1972 and spelled the death of slide rules. The price was $395, but in about five years Texas Instruments had a similar calculator available for around $20 - $25.

[NachoMahma]

.  Good counter-point. ;)
.  heehee Here's my mid-life crisis car (the date on the pic is a year off):

[Phil B]

I have been driving a bronze-colored Olds Alero for better than ten years. One day I began to notice how good those look in red. I thought I wanted one. Soon I noticed the red Aleros were driven by bubble gum popping, cell phone wielding young teeny bopper girls. That killed my interest in a red car.