Selling a Sliderule
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7 January 2014
This guide is written for the person who wants to sell a sliderule but is unsure of what information is relevant. The following may help.
To make your listing easy to find, include the words "Slide Rule" and "Sliderule" in the title, followed by the make and model number, if known. For example "Slide Rule, Sliderule, Aristo 0972 Hyperlog".
Make and Model
There are dozens of makes and hundreds of models. In most cases this information is prominently shown on the body of the rule, others have it on the centre slide or occasionally hidden in the gutter under the slide, so look carefully on all surfaces. An internet search for "international slide rule museum" will show a site with slide rules organised by brand name and country of origin. It has hundreds of photos and descriptions that may be of help with identification.
If you can't identify it, then clear photos will be helpful to potential buyers.
Good photos will not only help sell your rule, but they can make a significant difference to the price you get.
If you list with only one photo, show the front of the rule. preferably on a neutral background. However, most buyers will want to see the front and rear faces, the cursor (particularly if branded), any scales on the rear of the centre slide, and any marking in the gutter under the slide.
Make sure images are in focus. The scales and any other engraving or text on the rule must be readable in the photo. If a potential buyer can't read the scales then the photos aren't good enough.
Use the macro setting on your camera for close-ups.
Use good lighting. Don't use flash. It will spoil your photo. Diffused natural light will give much better results.
Upload the maximum size photo that eBay will allow. That's currently 7MB.
You can also get excellent images using a good flat bed scanner, but cheap scanners give less satisfactory results. Most slide rules will be longer than the scanner bed, so you will need to scan two passes to get the whole rule.
Check your listing. I'm amazed at how many sellers skip this basic step and list with out of focus, dim, or upside down photos.
If you look at the left hand end there should be a series of letters marking the scales. A few sliderules may be missing these letters, but most will have them. Common scales are A,B,CI,C,D and K, but many others are possible. Just list them in order from top to bottom, like this:K,A,B,CI,C,D etc. If the rule has scales on both sides, list both sets of scales. Some single sided rules may also have a set of scales marked S.L.T on the reverse side of the slide. Most scales will be black, but the CI will usually be red. You should mention any scales marked in other colours.
When the slide rule is correctly assembled the 'C' scale on the slide will be adjacent to the 'D' scale on the body.
This is the glass or plastic window which slides over the length of the rule. The scales are read through it using one or more hairlines marked on the inner surface. Unfortunately, cursors are often missing. Apart from a few specialist models, a sliderule without a cursor has little value. A damaged or badly scratched cursor will reduce the value of the rule, but it may be suitable to fill a gap in a collection.
If by some rare chance you have an undamaged cursor on a damaged rule, offer it for sale. Collectors are always seeking good cursors.
Some owners write their name, initials or other custom marks on the sliderule or its case. Any marks made on the rule by an owner should always be declared in the listing. Never attempt to remove them.
Condition should be apparent from your photos, but the following are worth addressing in the description.
Are the scales sharp and easy to read? Have they faded or bled onto the surrounding surface?
Is the rule stained or water damaged?
Is it bent, twisted or warped?
Are there burns, cracks, significant scratches or other marks?
Is any part of the rule delaminating?
Is the cursor present and intact?
Do the slide and cursor fit properly, neither too tight nor too loose? Do they move smoothly?
Are any original screws missing, either from the cursor or the body of the slide rule?
Defects should be declared in the written description even if they are visible in the photos.
Original accessories such as a case, instruction booklet, warranty or inspection certificate can enhance the value of the rule. However they must be correct for that model, and their condition is important.
Combining With Other Items
The only items that should share the listing with the slide rule are accessories that would have been supplied from the manufacturer, such as those mentioned above.
Unrelated items will increase the postage cost without adding value to the primary item. That usually means lower bids as the bidders take the postage cost into account.
Similarly if you have two or more slide rules to sell, it is usually better to list them individually. You can offer a combined postage discount if the same bidder wins two or more of your items.
As a rough guide, large rules will sell for more than small, and the more scales the better. But even some of the larger ones are fairly common, so be realistic with your starting price. Models intended for use in schools are generally at the low end of the value scale, only a few dollars. On the other hand, rare and desirable models can achieve sale prices over $1000.
Do not fall into the trap of listing your rule for an unrealistic starting price. If your rule is valuable it well get plenty of bids, but if you overprice it you will get none.
The heaviest slide rule I own weighs 425gm in its case. Most weigh less than 300gm. In many countries they qualify for Small Parcels rate, and can be posted anywhere in the world quite cheaply. Collectors know what postage is reasonable. Inflated postage makes you look dishonest.
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