[time-nuts] gnat sizing

[Steve Rooke]

I'm from the SE of England, Brighton and Ipswich, and this is the
measurement as I remember it from a very long time ago too Peter.

Steve - G8KVD <- that dates me just a bit & ZL3TUV

2009/8/23 Peter Vince <pvince at theiet.org>:
> Maybe I was brought up in a more genteel part of West London, but the unit of measurement I was brought up with was a
> Gnat's Whisker.  I don't think that was just my parents cleaning it up, as that expression seemed pretty common.  Sometimes
> abbreviated to just "a gnat's", but it was definitely its whisker that was understood.
>
> Peter Vince  (G8ZZR, London, England)
>
>
> On Wed Aug 19 22:49 , 'Lux, Jim (337C)' <james.p.lux at jpl.nasa.gov> sent:
>
>>I realize we are straying afar.. but inquiring minds may wish to know.
>>Referring to "A handbook of the gnats or mosquitoes: giving the anatomy and life history of the Culicidae" by George
> Michael James Giles, 2nd edition, 1902  (thank you google for digitizing this book from the Stanford library) The forward
> says that the second ed is much better than the first "...the result of a couple of months of constant work with the
> microtome." So I think we can consider this a reliable reference.
>>
>>Now I readily confess that this book seems devoted to only members of family Culicdae, and it's not clear that when
> referring to gnat anatomy as an unit of measure whether these are the gnats being referred to. The common name gnat
> seems to be applied to many small (often biting) Dipterid Insects, and Wikipedia seems to restrict the gnat terminology to
> other families.
>>
>>It would appear that the rectum of the gnat is about 1/10th the diameter of the abdomen (there's a drawing of a transverse
> section of the abdomen on page 91). If the page is about 6" wide (judging from the type size, and the image of the checkout
> card in the back page this is reasonable.. it's probably octavo size), then the 100x drawing is 2" across, so that rectum is
> .002 inches across (call it 0.05 mm, or 50 microns) .  This is much larger than the 1E-4 inches (2.5 microns) previously
> cited, but well within the range for human hair diameters (given as 17 to 181 micron in a variety of online sources, but a
> much smaller range of 50-90 micron is cited in "Forensic Examination of Hair", albeit for scalp, J. Robertson, Ed.)
>>
>>Now, to return to the original question of position accuracy for your timing receiver.  Whether 50 microns will result in a
> significant timing error? 1 nanosecond is 300 mm light time. 300 microns is 1 picosecond, so that 50 micron position error
> is down in the femto seconds..
>>
>>
>>James Lux, P.E.
>
>
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-- 
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.