John's Slide Rules: Under construction

Link to Thornton/P.I.C. Slide Rules

I hope that this site will some day serve as a reference for those interested in Thornton/PIC slide rules. It's fairly rough now, but will improve with time.

If you have any Thornton/PIC slide rules in your collection. I'd like to hear from you. I particularly want to establish a timeline which shows changes in the models, features and cursors used. Scans of your rules will be most welcome. Contact me at

How the scans were made:

Only scanners with a good depth of field are suitable for scanning slide rules. There is a good explanation here about the sort of scanner needed for 3D objects.

The black background was obtained by scanning with the lid open.

A 10” slide rule is too long to be scanned in one pass, so two passes were made and the two images stitched together in photo editing software. It is vital that the slide rule is exactly parallel to the long axis of the scanner otherwise the two images will not stitch seamlessly.

Scanning resolution was 300dpi, and the final image was shrunk by 50% in each dimension to reduce the image to a manageable size for web hosting. I used the Windows XP Image Resizer power toy, but there are several other free utilities available to do the same job.