Histograms (Fibre Test Results)
AFD (Average Fibre Diameter): average thickness of each hair in microns (1 micron = 1/1000th of a
millimeter or approx. 1/25,000th of an inch)
SD (Standard Deviation): the amount, in microns, away from the AFD where the majority
of fibre diameter values fall. The actual range is actually twice the SD, i.e. if
the SD is 5 and the AFD is 25 then the range is 10 microns from 20 to 30 microns (5
microns below the AFD and 5 microns above).
CV (Coefficient of Variation): a comparison of SD to AFD, expressed as a percentage.
Formula: CV = SD/AFD x 100 (see below)
%>30: the percentage of fibres that measure over 30 microns in diameter
(thickness). This is an indication of how many "prickly" hairs there are
in the fleece.
The lower number the better for all 4 values above.
Comfort factor: the %>30 subtracted from 100. ie. if the %>30 is 5, then
comfort factor is 95% (100 - 5).
Handle: is the "feel" of the fleece. A soft feel means good
handle, which is the result of an even fleece or low SD.
CV DEBUNKED: Don't be fooled by a higher CV. It can be higher because of a
very low AFD! An AFD of 20 microns is very fine! An SD of 5 microns is good,
which means the majority of fibres fall between 15 and 25 microns in diameter (5 microns
below the AFD and 5 microns above the AFD). I don't agree that fleeces can be
compared by CV's alone, in fact I would throw out the CV altogether! Comparing CV
(coefficient of variation) means that you are allowing a wider range of hair thicknesses
(higher SD = less even fleece) the higher the AFD is. A higher AFD means coarser
fibre (not good) and a higher SD means less even fleece (also not good). The lower
number the better for AFD, SD and %>30 microns. But a low CV (eg. 20) could just
mean the AFD is high! CV is a percentage: SD divided by AFD multiplied by 100.
There is no reason to allow a wider range (less even fleece) just because the AFD
is higher! A coarser fleece can still have good handle (soft feel) if it is an even
fleece (i.e. has a low SD). Comparing CV's is the same as saying, "This coarse,
uneven fleece is just as good as that fine, even fleece!" NOT TRUE!
For example, 2 fleeces:
Fleece A: AFD 20 microns, SD 5 (both good values - a very fine, even fleece),
resulting CV is 25 (sounds a bit high but the majority of fibres are between 15 and 25
microns - pretty fine!)
Fleece B: AFD 35, SD 7 (both high, ie. not great), resulting CV is 20 (sounds
better than fleece A but this fleece is very coarse and uneven as well. The majority
of fibres are between 28 microns in diameter, which is above "comfort" level and
42 microns - extremely coarse.)
I would MUCH prefer fleece A, wouldn't you?