My son found this in the dirt near his house today. I don't recall ever seeing one before. Anybody?
Circular slide rule
My dad used to carry one along with a book of natural sin tables. Used it to reduce slopes in the field.
I used it to cheat in math... 🙂
N
Awesome..........
Commonly used by electric coop guys to calculate guy wire installations.
I spent a few years at a consulting firm dealing mainly with construction contract administration and oversight.?ÿ From time to time between projects the engineers would use me to help put together their next project.?ÿ One old crusty engineer?ÿin particular, Ol' John,?ÿrequired me to keep notes on anything I calculated...from quantities to storm water control design.?ÿ He would always make me sit in his office as he reviewed and critiqued my?ÿnotes.?ÿ Being that John graduated school well before WWII even started, I felt more like a schoolboy than?ÿanything else.?ÿ
One project in particular?ÿincluded a couple of dozen storm structures and John needed me to justify the size of the culverts.?ÿ His preferred weapon was the "rational method".?ÿ I fought through several of the structures and was close to being convinced that gravity hydraulic flow in a closed conduit is more witchcraft than anything else.?ÿ One day I was digging around in the desk I used and found a little round "calculator" like?ÿthe one shown above, but it was from a local?ÿreinforced concrete pipe?ÿmanufacturer.?ÿ With just a few numbers dialed in such as drainage area, slope?ÿand friction coefficient, one could flip the little disc over and read the size of pipe required to handle the "Q".?ÿ I loved it.
When John got around to reviewing what I had come up with he wanted to see my "notes".?ÿ I tossed the little round calculator on his desk.?ÿ He ranted and raved about how absurd any such thing might be.?ÿ I told him I had checked it against his rational method and it was awfully close.?ÿ I suggested he try it for himself.
I didn't hear any more friction from him and our project proceeded.?ÿ A couple of months later I caught John digging through the drawer on my drafting table.?ÿ I asked him what he was looking for and he asked, "Where's that neat little round thing that figures pipe sizes?"?ÿ ??ÿ
When I was a neophyte the company I was with hired an older, retired P.E. I remember that he used to sit with a circular rule in one hand and manipulate it deftly. I said something to him about his one-handed skill with it and he began reminiscing. He had learned to use it one-handed when he was under fire in the Philippines in WWII. He also recounted that he had used that rule to perform all of the roof beam designs in the roof of the Colosseum building in Phoenix, AZ. He explained that the roof was a hyperbolic parabaloid - hyperbolic in one axis and reversely parabolic in the other (you have to see a picture to understand it). All the design was performed with that rule and a 12-place book of trig tables. It impressed me then and it still does.
I spent a few years at a consulting firm dealing mainly with construction contract administration and oversight.?ÿ From time to time between projects the engineers would use me to help put together their next project.?ÿ One old crusty engineer?ÿin particular, Ol' John,?ÿrequired me to keep notes on anything I calculated...from quantities to storm water control design.?ÿ He would always make me sit in his office as he reviewed and critiqued my?ÿnotes.?ÿ Being that John graduated school well before WWII even started, I felt more like a schoolboy than?ÿanything else.?ÿ
One project in particular?ÿincluded a couple of dozen storm structures and John needed me to justify the size of the culverts.?ÿ His preferred weapon was the "rational method".?ÿ I fought through several of the structures and was close to being convinced that gravity hydraulic flow in a closed conduit is more witchcraft than anything else.?ÿ One day I was digging around in the desk I used and found a little round "calculator" like?ÿthe one shown above, but it was from a local?ÿreinforced concrete pipe?ÿmanufacturer.?ÿ With just a few numbers dialed in such as drainage area, slope?ÿand friction coefficient, one could flip the little disc over and read the size of pipe required to handle the "Q".?ÿ I loved it.
When John got around to reviewing what I had come up with he wanted to see my "notes".?ÿ I tossed the little round calculator on his desk.?ÿ He ranted and raved about how absurd any such thing might be.?ÿ I told him I had checked it against his rational method and it was awfully close.?ÿ I suggested he try it for himself.
I didn't hear any more friction from him and our project proceeded.?ÿ A couple of months later I caught John digging through the drawer on my drafting table.?ÿ I asked him what he was looking for and he asked, "Where's that neat little round thing that figures pipe sizes?"?ÿ ??ÿ
Had one of those, it applies the Manning Formula (Q=1.486/N*A*R^2/3*(squrt S)) to the slope and N to get pipe diameter.?ÿ It was developed by a Swiss Engineer for open channel flow but is commonly applied to pipes.
The Rational Method (Q=CiA) is for calculating storm water flow, typically for a 10 year storm. My old boss (a PE) used to call it the Irrational Method.
Placer County had a lot of trouble during the 1986 flood.?ÿ The storm drainage manual called for an "initial time of concentration" which reduced the Q amount.?ÿ They eliminated this.?ÿ In the next flood event the pipes were much larger so everything got flooded downstream.?ÿ After that SNAFU they hired an Engineering Consultant to update their storm drainage manual.?ÿ There is a lot of storage in ditches on the upstream side of culverts if the culverts aren't too large, the storage attenuates the peak flows.
Whether it was planned or not nobody knows.?ÿ But a lot of early county maintenance around here?ÿincluded "ditch detention".?ÿ
County road maintenance has always been an underfunded affair.?ÿ Crossing structures were few and far between and woefully undersized.?ÿ Any time there was a toad-strangling rain the undersized pipe (and road)would get washed away.?ÿ The work around involved, as you described, wide and relatively flat upstream channels that held the peak flow and allowed it to be released through the undersized structure.
We always referred to them as the "county detention ponds".
Interesting and informative post. No information from me about that, but Paden posted, "We always referred to them as the "county detention ponds".
I had to laugh because any retention/detention/big swale or large ditch that holds water for 3 hours or so in Florida subdivisions is considered (by realtors) as a "Waterfront Executive Estate" lot.