Decipher this Specification
Decipher this Specification
(OP)
"The visual warning required... must be installed such that it does not require more than +/- 15 degress side-to-side head rotation as viewed..."
Do you interpret this as meaning (A) a total of 15degs of head rotation (7.5degs left & right), or do you interpret this as (B) a total of 30degs of head rotation (15degs left and right).
Do you interpret this as meaning (A) a total of 15degs of head rotation (7.5degs left & right), or do you interpret this as (B) a total of 30degs of head rotation (15degs left and right).
"But what... is it good for?"
Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip.
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?





RE: Decipher this Specification
RE: Decipher this Specification
Hg
RE: Decipher this Specification
"But what... is it good for?"
Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip.
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: Decipher this Specification
TTFN
RE: Decipher this Specification
Hi MadMango,
I hope, for your companys sake, that the others involved in the discussion, are not responsible for any engineering decisions. Thats pretty basic "cast-in-stone" stuff to be debating.
±.002" = total .004"
+.005"/-.002" = total .007"
RE: Decipher this Specification
Stephen A
RE: Decipher this Specification
RE: Decipher this Specification
I have to disagree. To me, "plus minus 15 degrees" when spoken means +15/-15 degrees = 30 degrees. To interpret it as 7 1/2 degrees each way you would say "15 degrees plus or minus".
RE: Decipher this Specification
RE: Decipher this Specification
But more confusing to me is the term "as viewed." It would make more sense if it read:
"..must be installed such that it does not require more than +/- 15 degress side-to-side head rotation to be viewed directly..."
Or something like that. Without turning the head at all there's almost a 90 degree field including peripheral vision. Maybe it makes more sense in context.
--Jonathan
RE: Decipher this Specification
I thought I clicked preview rather than post. Obviously not, otherwise I would have caught the two mistakes in the first sentence. Degrees. Approximately.
RE: Decipher this Specification
I suspect that what was elided after "as viewed" was something like "from the front" or "from above", as a means of defining "side-to-side", as opposed to an observation method.
Hg
RE: Decipher this Specification
The funny thing about these wonderful Federal requirements is how poorly written they actually are. As some must have noticed, there is no specification of head rotation in the vertical plane, only the horizontal.
"But what... is it good for?"
Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip.
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: Decipher this Specification
TTFN
RE: Decipher this Specification
"But what... is it good for?"
Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip.
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: Decipher this Specification
TTFN
RE: Decipher this Specification
Then there are the documents produced not only by engineers, but by higher-level engineers who aren't the people who have to deal with and interpret or enforce the document every day.
Hg
RE: Decipher this Specification
Additionally, there is the desire to KISS, but you wind up with a less specific and contained requirement. The example requirement here could take a full page to completely specify, which means that you'll need to verify each and every condition and sub-requirement, which is quite monumental, particularly if it's a small portion of an overall system.
Overall, it's a complicated game of "catch me if you can." When you write a requirement, there is a tendency to have a mental image of what you're specifying. When you simplify the requirement, it's often based on the that mental phantom, but the supplier is under no obligation to design that particular embodiment, and thereby provide a product that's operationally unacceptable.
TTFN
RE: Decipher this Specification
Hg
RE: Decipher this Specification
If there's plenty of margin, then it's usually not a big deal, but often, the specification pushes the limit of the design and then, you get into a BIG, prolonged hashing of tolerances and how they are accumulated, e.g., RSS or added and what did we really sign up to in the first place.
TTFN
RE: Decipher this Specification
I take tolerances as an absolute. If they just barely missed it, they still missed it; the edge of the tolerance isn't what they should be aiming for anyway. The tolerance is how much they can just barely miss some other target by.
The stuff that gets to me is language like "should be nearly parallel". Thanks, I can really enforce that.
Hg
RE: Decipher this Specification
TTFN
RE: Decipher this Specification
My personal favourite was a project for which the client specified a "super-flat" concrete floor slab, because the equipment that was to be installed required extremely precise alignment. When we asked for allowable tolerances on construction and subsequent in-service movements, and explained that the term "super-flat" doesn't have any universally accepted definition of allowable deviation from nominal alignments, the client came back with +/- 0 mm, and was absolutely immovable on that point. (+/- 0 flexibility or common sense!)
We never did get the client to relax the specification, so we declined to bid for the design and construction management. Presumably, he found someone who had EXCEPTIONAL concrete construction capability. (Or more likely, they never checked the construction tolerances, or else they did, and ended up in a long and bitter legal battle!)
RE: Decipher this Specification
Wow, MadMango,
You really stared something here ... 24 posts (±1) in 24 hours ... not bad
RE: Decipher this Specification
+/- 0 mm over what area?
I could lay a "super flat" floor of +/- 0 mm over any given area of 0 m^2.
Just think of all the money you could have saved on shims had you bid the job!
RE: Decipher this Specification
Hg
RE: Decipher this Specification
RFF
Really F***ing Flat
RE: Decipher this Specification
Hg
RE: Decipher this Specification
Putting Human Factor Back in Engineering