Is super-accuracy matters?

[Johnh]

This is a nice thread, and so I'd like to show you something very personal from my family. In the late 1800's, my great-great (great) uncle was a young engineer working on the mechanism for lifting the decks of Tower Bridge in London. After that, he set off around the world on a career as an engineer in the British Empire, in southern Africa and eventually in New Zealand.

He took with him his Fullers Cylindrical Sliderule, and I have it here. While sliderules were usually about 12" long and could with care, offer accuracy to about 3 digits, this one is accurate to 5 digits. This was done by using a set of very long scales wrapped in a spiral around a pair of concentric cylinders. Effectively, the scales are over 40' long.

Ours was made probably around 1898, here it is:

   

Its beautiful made from fine hardwoods, with scales printed and then bonded. The two cylinders move smoothly with what feels like a layer of velvet between. Precisely machined brass bars get aligned and then read against the printed scales.

So how accurate is it really?

Consider a calculation with quite a lot of digits involved, such as 1.2345 x 2.3456

Here is the setting of the two input numbers:

   
   

And the result (with a 21st century calc app)

   

You can clearly read 289 printed just to the left of the pointer, the scale for the next digit 5, and interpolate quite clearly for the 5th digit 6 , so 2.8956 !

I find it amazing, firstly that someone could conceive of this device in the 19th century (George Fuller, professor of engineering at Queen's College, Belfast, patented in 1878), and then that it could be made accurately enough so that it worked.

Ours is in remarkably good condition, almost 'New in Box'. This suggests to me that it's possible that none of my ancestors every really got around to figuring out how to use it! though we do have a printed manual.

Apparently these were made up into the 1970's, with different materials such as Bakelite, a production run of almost 100 years. So they crossed over with the early HP scientifics and making the 40-year-old design of my HP15C look like new tech!

The device is covered in a few websites, but here is a nice one, featuring a collection of other interesting old calc tech:

https://www.pghtech.org/news-and-publica...20or%20two.