Slide rules for use in the field or office were standard tools for the surveyor. And specialty slide rules, with specific scales for use in tacheometric - or, stadia-metric -calculations, were sold by several manufacturers.

Detailed discussions of the use of tacheometry may be found in Appendix 1 and Appendix 2.

The degree is a unit of plane angle equivlent to 1/360 of a circle It is widely used in most slide rules using trigonometry.

The system is often referred to as 360^o.

The gon (also called the grad, grade or sometimes quite dangerously the gradian not to be confused with radian) is a unit of plane angle equivalent to 1/400 of a circle.
The system is often refered to as 400^g. It is based on the metric system since a quadrant is 100 units in this system whereas it is 90 units in the convention 360^o system.

The 400g system is widely used on slide rules for tacheometric work especially in the European nations.

Rod Lovett

Born in Leicester, England, in 1940, I have spent most of my life in London and the South East of England.

From an early age I wanted to be a teacher - my uncle was a fine linguist and teacher. At school I came under the influence of a fine Chemistry teacher and at University under the influence of two outstanding Physics teachers and followed them into this profession. The first five years of my career was spent lecturing in Physics at Goldmsiths' College London University and these years have left an indelible impression on me of the beauty of Mathematics and Physics.

Throughout these years my trusty Aristo 0903LL which I first bought at sixteen when I was at school was always by my side. Sadly it was obvious even in the middle of the 1960's that the number of students going into Physics was declining (a decline that accelerated rapidly as the years progressed) and rather than becoming disheartened at limited career prospects I decided to change subjects. I knew nothing about computers - very few people did - but it looked interesting so I joined a mathematics department at a College in East London that had one - an Elliot 4120. It had an Algol compiler which had to be loaded (twice!) from paper tape for each compilation and I became an expert at mending ripped paper tapes. This was the last time I used my slide rule in earnest.

After a year I moved to another college, Kingston upon Thames , where I completed a Master's degree in Computer Science and stayed for the next 35 years teaching Computer Science. Here we also had an Elliot 4120 with paper tape input but with the incredible luxury of compilers on magnetic tape. No discs! As the years progressed more and more sophisticated computers arrived.

In the early 70s I obtained a Unix license from Bell Labs (it took me 18 months and I had to jump through hoops to get it!) - I think it was for Version 6 - and I still have the license somewhere. In those days it was free to educational establishments but cost a fortune to the commercial world. For about ten years apart from my teaching I was also a Unix system administrator, first of all on a PDP - 11 and later on a network of Suns. It was on the PDP - 11 that my son and I (my daughters were too young and didn't become interested in computers until after they left school) played a wonderful game called Advent. Long before PCs and graphic cards this was one of the first computer adventure games and totally text based. It took us many weekends to map "Colossal Cave" and often we were "in a little maze of twisty passages, all different".
BR> It was during this time in the 1980s as a Unix system administrator I learned the language Perl that was to be so valuable in developing my web site fifteen years later. Quite amazingly Perl was not developed for Web programming ( obviously. since the web and web programming had not been born ) but when the time came it was the perfect program for web development.

I had been meaning to start collecting rules all through the 80's but it wasn't until the late 90's that, with retirement beckoning, and no current hobbies, I decided to put into effect a thought that I had been nursing for some years - to collect slide rules. Obviously I would almost certainly be the only person on the planet to have such a ridiculous idea and so without much hope of success googled (or more probably used Alta Vista since Google wasn't as all powerful as it is now) for "slide rule". To my surprise I found there were an amazing number of like - minded lunatics, some eagerly waiting for a book by one Peter Hopp due to be published shortly.

I bought it, went up to my loft, found the slide rule that I had first used at school and later as a student at college, my trusty Aristo, with my initials scratched into the plastic end piece, horrible!, and caught the bug. I was hooked. Initially I was a general collector but now it's mainly Aristos. For legibility with weakening eyes in poor light I find them incomparable - engineering at its finest.

In the 1990's as I started collecting slide rules I thought that I would just put the pictures of my rules on my site but one of the first sites on the net that I visited was Ron Manley's site and I found his slide rule prices of eBay auctions very useful. However, it didn't do exactly what I wanted. I decided I needed a searchable database rather than static pages. Ron kindly gave me his data (he had two year's worth at this point) and I wrote a Perl program to allow me to search it using quite simple to quite complex requests. This proved so useful that I quickly wrote another program (Perl of course) to capture eBay's data for completed auctions on eBay.com so I wouldn't need Ron's data. Since I found it useful, I assumed other people would so I made it available to everyone. Later I extended it to display data from eBay.co.uk , eBay.de and eBay.fr and have continued to add extra facilities to it (price bar graphs etc.) as the years have gone by. From that point for many thousands of hours I have gone on to develop a very wide range of facilities for slide rule collectors.

Full details of the development of my Web site up to 2017 can be found at: https://tinyurl.com/2p9xcupj and I now spend a significant amount of time developing, extending, and maintaining various slide rule data bases and search facilities not just on my site, https://sliderules.lovett.com but also on one of the Oughtred Society's websites, https://osgalleries.org (which leads to an array of links), which is available on my server. Editorship, co-editing the UKSRC Slide Rule Gazette with Peter Hopp is also interesting and quite time-consuming.