Change Log

March 8-16, 2023

I uploaded initial images of the Oughtred Circles of Proportion replica, with commentary surrounding that instrument updated over the course of a week.   Also a PDF for the front face of the calculator.

It's been a long while since my last upload.  My electronics hobby was occupying me for the most part during the Covid pandemic.  I'm attempting to use a better method to generate the scales, involving external data specifications of the scales.   

My replica is based on the  Robert Davenport interpretation.  Davenport was a Scottish instrument maker, and the National Museum of Scotlands photos of it are the clearest photos of any Oughtred instrument I can find on the internet.  The front page for the Oughtred Instrument is here.      

August 15, 2021

I uploaded a new photo of the homemade slide rule I found in an antique store to my 'unusual slide rules' page.    It means a great deal to me, and I should have placed it there ages ago.   It's surely unusual.

May 6-7, 2021

I added a page describing the 'Steffens method', a new (to me) tactic for implementing my favorite style of circular slide rule: two cursor long scale models.   I probably need to change other pages on my site to bring this method into play for earlier models I've attempted.     A few more updates to the J Michaelson page;  I think I finally have that model working.    I will have to tidy up the PDF files and maybe upload the 3D STL files at some point.

May 5, 2021

Some small edits to the J Michaelson project page.    I uploaded my new favorite special slide rule,  the Magnum Double-Log Long-Scale Calculator - Log-Log-Spiral-Rechenscheibe by Oliver Steffens, on the unusual slide rule page.   And of course... this new page added because the log was finally getting too long for the main page.

May 4, 2021

Uploaded the first version of the Michealson instrument.    A few problems remain, but I trust the calculator is otherwise pretty close.    The gearing mechanism appears to work nicely, just needs to bit less slack.

April 22, 2021

I added a work-in-progress page for the Joseph Michaelson patent, a bit more info on spiral scales, and a page on the Lilley improved calculator patent.   Lilley's calculator is nearly identical to the GM Andrews calculator, so I didn't attempt to do a separate replica of it.     Also, a page on how the "L" scale works with Spiral scales.

April 4, 2021 

I completed the write-up of the GW Andrews calculator.   A final PDF with build and operating instructions is now uploaded.  

March 20, 2021

Whoops!  I failed to announce the 'Slide Rule as a Status Item' page, which went up some while back.   

March 16, 2021

Uploaded replica scales for an SR patent by GW Andrews, a nice Archimedean spiral model with a turn counter.   Cleaned up numerous grammar errors in the Macdonald SR pages from the previous update.

Oct 22, 2020

Uploaded replica of a patent for the Macdonald Logarithmic Spiral based slide rule.    Completed the Nystrom write-up.

August 2020

Nystrom Calculator replica uploaded.

May 8, 2020

Switched to left-hand side menus for compatibility with mobile browsers.   

May 4, 2020

Some revisions  to  the 'Materials' page under Making Slide rules at home

April 28, 2020 - Updates "new" Google Site released.   

This is a redesign of content on the original site, using the new Google Site templates. 

New content includes a Nystrom Calculator replica and some pages with selections from my SR collection.

New Pages:   Items from my collection,   Slide Charts and Specialized Calculators,  Advertising (Gift) Slide Rules, Unusual Slide rules,  The Nystrom Calculator