Yes the boring factoid is that the original Fahrenheit scale is a centigrade one, because he divided the difference in temperature between hot ox blood and some (rather good) freezing solution into 100 parts.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376
And here I was told that the SI crowd was miffed because the Imperial scheme recognized the guy who invented it, Daniel Gabriel Fahrenheit, while their inventor's name was consigned to oblivion out of some pragmatic desire to give only descriptive designations to SI units and so they were stuck with Centigrade. That is until some bright fellow pointed out that since they BOTH began with the letter 'C', that there was no reason that they couldn't quietly drop Centigrade and replace it with the name of the genius who first proposed dividing the range of freezing to boiling points of water by 100, Anders Celsius.
I kind of like my story better ;-)
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
The Imperial measurement system has only been standardised since 1824 so serving us well for centuries is rubbish maybe 1 1/2. Before that nonstandard units created chaos.
You know you're an engineer when discussing units of measure is a good pub topic...(for the record, I have this exact conversation with engineering friends over a beer. Needless to say, I think we sounded pretty attractive to any nearby females that overheard the conversation.)
Comming from an "old" metric (SI) country i can say "its just a unit system". Its like driving in the right side of the road. You are not aware of the fact that since China&India is driving in the left side you will soon be a minority. This makes travel (to the countries where cars drive in the left side of the road) a little dangerous, but you will learn it fairly quickly if you need to.
Tires are mixed 205/60-15.
205 is the width in mm
60 is an aspect ratio of width to sidewall height
15 is the rim/sheel mopunting diameter in inches
How this system has evolved into the mixed unit mess it is is beyond me. I know Society of Automotive Engineers standards have something to do with keeping it alive, but why not change the wheel to mm, 15" becomes 380mm. now you have 205/60-380 tire size.
"Wildfires are dangerous, hard to control, and economically catastrophic."
It's same reason why sparkplugs have always been metric even when the rest of an American automobile was in Imperial units back before that industry made the move to metric or why the hose connections on all fire hydrants and fire trucks around the world use a standard based on Imperial units. Sometimes tradition, as in the case of Sparkplugs and Wheels, is the reason while in others, like fire hose connections, is the result of society being unwilling to take the chance that in an emergency a borrowed set of hoses will not be compatible with the local fire hydrants or the equipment available to fight a fire.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
It runs out that camera threads are 1/4-20BSW, and have been for something over a century. 1/4-20UNC screws work, but they were not available when the specification was worked out.
I'm from California, so I grew up on the US Customary system. I learned a little SI in junior high school science and quite a bit more in high school Chemistry (taught by my father) and Physics (taught by a brilliant man who was a scientist for the US Navy during WW2). Both classes used SI exclusively and both teachers insisted on units for all calculations.
In college (I graduated in 1980), Chemistry was 100% SI, Physics was about 60% US/40% SI, and my engineering classes were the other way around at about 60% US/40% SI. Some professors were sticklers for units, others (for some reason) were not.
Through education and work experience I am mostly conversant in SI, but by virtue of living in the US I am more comfortable with US Customary units. I can visualize some SI units, but certainly not all, while I can visualize almost all US units.
That being said, I would much prefer to work with SI units exclusively because they are internally consistent and easier to work with. However, because I use Mathcad quite a bit, I can mix and match units without having to worry so much about the fine points of converting units.
I was project manager or project engineer for the civil design for six federal projects: three federal prisons, two buildings at a naval air station, water system improvements at an Air Force base, and a fire protection pipeline at a Marine Corp base. I was also the project quality engineer for an infrastructure upgrade project at an existing federal prison. All of these projects were designed and drawn with SI units, but it wasn't all smooth sailing. Two stories about this:
FIRST STORY
On the prison projects, the architect we were working for and his other consultants were fully SI capable, so the design process went smooth enough…well except for the dumbest drafter in our office who asked for my help because he didn't know how to draw a 4H:1V slope in metric (no joke). It's when the plans got to the field that problems began.
During the bid phase for the first prison project, I took a call from a confused contractor. He was having trouble with our storm drain design. The meat of the conversation went something like this:
Contractor: So, a 1200-mm pipe is a 48-inch, right?
Me: Yes.
Contractor: With a 5-inch wall [this was reinforced concrete pipe], that puts the top of the pipe 4.42 feet above the invert, right?
Me: Yes.
Contractor: But your invert at Pt#xxxx is 40.00 and the grading design shows a finished ground surface of 42.75. That puts the top of the pipe about 1'-8" above ground.
Me: No. All vertical information is in metric units. [I found most contractors haven't heard of SI, so I use "metric".]
Contractor: Whaddya mean the vertical information is in metric?
Me: The entire project uses metric units. Pipe cover at that location is about 1.4 m or 4.6 feet.
Contractor: Oh. So everything is in metric?
Me: Yes.
Contractor: Well, I'll be damned.
Next, the grading subcontractor's surveyor busted the US-SI conversion at the project benchmark. Actually, he did the conversion right, but he made a typo in his calcs that resulted in him being 1 foot off. I found out about this at the first partnering session when the contractor claimed there was about 200,000 CY of extra excavation than he had not planned on. As you can imagine, everyone from owner to architect to contractor was VERY worried. I wasn't because I knew our data and deesign were good, plus I suspected a US-SI conversion problem. I got permission to talk directly to the surveyor when I got home. The surveyor sent me his electronic files, including his ground topo map. By comparing about a dozen of his shots on existing concrete with our topo, I determined that the error was exactly 1.00 foot and not some random error. I then called the surveyor and told him what I had found and I asked him to walk me through his surveying set-up, including how he had handled the benchmark. That's when he spotted his error. He had (for example) noted a benchmark elevation of 152.35 feet, but his next calculation used 153.35 feet (a simple typo) for the conversion to SI. Ten minutes work and I looked like a hero.
During construction I had numerous small issues like this because both the contractor and the CM folks for the Bureau of Prisons insisted on working and thinking in US units.
SECOND STORY
The project at the naval air station only worked because my project engineer and I were competent with SI units. This was a design-build project. During the proposal phase, we sent our site layout designs to the architect so he could review them with the contractor. While I was out of the office, my project engineer got a frantic phone call from the architect, who said they were unable to scale our drawings. He said they couldn't match our dimensions with 10-scale, 20-scale, 30-scale, 40-scale, any architectural scale, or anything else he and the contractor were familiar with. The rest of the conversation went something like this:
Project Engineer: The drawings are in SI units.
Architect: Whaddaya mean they're in SI units?
Project Engineer: The drawings are in SI units.
Architect: WHY are the drawings in SI units?
Project Engineer: Because that's what the RFP requires and the survey the Navy the provided is in SI units.
Architec: But we don't have a metric scale.
Project Engineer: We got ours at OfficeMax.
Even so, we ended up winning the project. In the middle of the project kickoff meeting, the architect asked the Navy's project manager if SI units were still required or if the project could be done in "regular" units. The Navy's PM said "I don't like metric and my people don't either, so let's design this with "regular" units."
I raised my hand as said,
Me: As the civil engineer, I don't have a preference. However, the topo survey the Navy provided is in metric and I'm not willing to take on the liability of converting it to US units. Is the Navy willing to have the surveyor of recond convert the survey?
Navy PM: Why can't you convert the survey? We don't money in the budget to have the surveyor change the survey. [I found this hard to believe since the total project budget was $14M and the survey conversion could probably be done for several thousand dollars.]
Me: First, our firm does not do surveying. Second, converting the survey carries a liability I can assure you I will not get permission to take on.
Navy PM (in the best tradition of Solomon): Well, we can do the civil work in metric and the building can be designed in regular units. [no joke]
Me: Even though I think this is a bad idea, I know that my project engineer and I can make this work.
And we did, with no help from the architect. Fortunately, I was able to increase my project coordination task budget enough to cover the additional effort on our part.
==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill
So, are you saying that the US cannot convert to SI units because the contractors, architects, and project managers are too stupid? I've heard a lot of reasons, but never that one.
