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.

Make and Model

The first thing a collector will want to know is the make and model of the rule. There are dozens of makes and hundreds of models. Many rules have this information prominently shown on the face, others have it hidden in the gutter under the centre slide. So look carefully on all surfaces. Include this information in your listing title, for example "Sliderule, Aristo 0972 Hyperlog".

The Scales

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 any other colours.

The Cursor

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.

Owners Marks

Some owners write their name, initials or other identifying marks on the sliderule or its case. Any other marks made on the rule by the owner should always be declared in the listing. Never attempt to remove them.

Condition

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.
 
Accessories

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

Slide rules are often listed together with drawing instruments, scale rules or other unrelated items. There may be a few collectors interested in these things together, but most are not. If you want to maximise your return, list the unrelated items separately. 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. The only items that should share the listing with the slide rule are accessories that would have been supplied from the manufacturer, such as the appropriate instruction booklet.

Photographs

Clear photos will help sell your rule.  Make sure they are IN FOCUS, and show the scales clearly.  Do not try to take a close up if your camera isn't capable. Avoid using direct flash; diffused natural light will give much better results. 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.

Remember that the images on eBay do not show much detail, so be prepared to email photos to prospective bidders, or host the images off site. Take plenty to email even if you only want one for the listing. They should show front and rear faces, the cursor, any scales on the rear of the centre slide, and any marking in the gutter under the slide. The scales and any other engraving or text on the rule must be readable in the photos.

Price

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.

If your rule is valuable it well get plenty of bids, but collectors may be reluctant to bid on a rule if the starting price is near the market value.

 Postage

The heaviest slide rule I own weighs 425gm in its case, most weigh less than 300gm. In most countries they qualify for Small Parcels rate, and can be posted anywhere in the world quite cheaply. Collectors know what postage is reasonable.

Please vote 'YES' for this guide if you found it helpful.