Glossary of Terms

Accuracy

A measure of the closeness of a test result to the true value. The true value of a measured quantity can only be determined by measurement systems that are calibrated by direct reference to primary references such as length, weight, force etc.

Airflow

A method of measuring the mean fibre diameter of a sample of wool in which a test specimen (a measured mass of the scoured, dried and carded sample or a measured mass of sliver), after exposure to a conditioning atmosphere, is compressed to a fixed volume and a current of air is passed through it. The rate of flow is then adjusted so that the pressure drop across the sample equals a predetermined value, or the pressure drop across the sample is adjusted until the air flow equals a predetermined value. The rate of flow in the first case, or the pressure difference in the second case, is an indicator of the mean fibre diameter of the wool in the sample.

Bias

A constant or systematic difference between a true value and corresponding test results. (Also see: Accuracy and Precision.)

Class Interval

The classes into which the individual snippet fibre diameter measurements are grouped, where the micrometre range of each group is identical, the micrometre value of each interval is an integer, and the micrometre value of the mid-point of each class interval is also an integer.

Coarse Fibre Content

The percentage of fibres in a Fibre Diameter Distribution which are coarser than 30 micrometres. (Also see: Comfort Factor.)

Coefficient of Variation

A statistical measure of the variability exhibited within a set of values. It expresses the standard deviation as a percentage of the mean; the higher the CV, the greater the variability. The coefficient of variation of a sample may be calculated from:

where		= coefficient of variation
		= standard deviation of the sample
		= mean of the sample

Coefficient of variation is often measured for fibre diameter, staple length and fibre length in sliver. (Also see: Fractional Coefficient of Variation.)

Comfort Factor

The percentage of fibres in a Fibre Diameter Distribution which are finer than 30 micrometres. (Also see: Coarse Fibre Content.)

Conditioning

A process whereby wool fibres are exposed to a conditioning atmosphere until the moisture absorbed by the fibres attains equilibrium.

Conditioning Atmosphere

A volume of air, capable of being maintained at standard temperature or humidity, or both, in which specimens are conditioned in a standard atmosphere. For wool testing this is usually a temperature of 20±2OC and a relative humidity of 65±3%. (Also see: Conditioning.) 

Confidence Limits

An expression of the precision of the mean of a set of values, usually associated with a stated probability, most often 95%. It is the interval around the mean within which, with the stated probability, the true value is expected to lie. 

Coring Tube

A tube of circular cross-section which is equipped with a sharpened, replaceable tip. The tip enables the tube to penetrate a bale of raw wool without rotation, remove a cylindrically shaped portion of the wool and retain it without change in material or moisture content. Very small diameter coring tubes may also be used to obtain fibre snippets for fibre diameter testing. (Also see: Minicore.) 

Cover slip

A very thin square section of glass placed over a specimen of snippets distributed over a glass slide, for measurement by Projection Microscope. (Also see: Mounting Fluid.) 

Crimp

The waviness of a fibre, expressed numerically as the number of complete waves per unit length; crimp is usually taken as an indicator of mean fibre diameter, the higher the number of crimps per unit length the finer the wool. 

Crimp Definition

The degree of alignment of the crimp waves within a staple. 

Crimp Frequency

The number of crimp waves per centimetre of staple length. Coefficient of variation of crimp frequency refers to the variation in frequency between staples within a lot. 

Curvature

The inverse of the radius of arc of a segment of a fibre snippet. Curvature is expressed as degrees/mm.

CVD

See Coefficient of Variation of Diameter. Distribution Histogram See Fibre Diameter Distribution.

Ellipticity

A term used to describe the shape of the cross-section of a wool fibre. It is quantified by assuming the cross section is an ellipse and calculating the ratio of the major axis to the minor axis. Circular cross-sections therefore have an ellipticity of 1. 

Fibre Diameter Distribution

The distribution of fibre diameter in a wool sample. Distribution can be expressed in the form of a frequency table or as a frequency histogram with data grouped into class intervals of one micrometre size, and integer micrometre values as midpoints of the class intervals. The results may be expressed in a number of ways including standard deviation, coefficient of variation and the percentage of fibres coarser than a given value such as 30 microns. 

Fibre Fineness

Used interchangeably with Mean Fibre Diameter. The term “Mean Fibre Diameter” in the context of wool fibres can be misleading, since it implies that wool fibres have a circular cross section. In describing the thickness or thinness of wool fibres it is more exact to use the term “fibre fineness”. The word “fineness” does not imply any particular geometry for the shape of the cross section. 

Fibre Optic Discriminator

A component of a LASERSCAN instrument used to ensure that the instrument only measures fibres that adequately intersect the laser beam. It consists of a circular array of 16 optical fibres surrounding a central optical fibre. Signals generated by the Optical Discriminator are also used to determine fibre curvature.

Fractional Coefficient of Variation

A statistical measure of the variability exhibited within a set of values. It expresses the standard deviation as a fraction of the mean. The fractional coefficient of variation of a sample may be calculated from:

where		= fractional coefficient of variation
		= standard deviation of the sample
		= mean of the sample

(Also see: Coefficient of Variation).

Frequency Distribution

See Fibre Diameter Distribution. 

Glass Slide

A rectangular section of clear glass, upon which snippets are dispersed for measurement by Projection Microscope. (Also see: Mounting Fluid.) 

International Wool Textile Organisation

A international forum for establishing standardised test procedures (IWTO Test Specifications), regulations governing the use of these procedures (IWTO Regulations), and procedures for arbitrating disputes over commercial transactions involving raw wool, wool sliver and wool yarns (the IWTO Blue Book). IWTO is pivotal in providing a technical and commercial framework for international and intranational trade involving wool. Representation within IWTO is via National Committees appointed by the Wool Industry associations within member countries. 

Isopropanol

Isopropyl alcohol is a three-carbon molecule within the family of chemicals defined as alcohols. It has the chemical formula CH3CHOHCH3 . It is a clear liquid and is used as the fluid medium for dispersing snippets for measurement by the LASERSCAN instrument. 

IWTO

See International Wool Textile Organisation Laser A device for producing a narrow intense parallel beam of light, with a specific wavelength.

Laser Beam

The light produced by a laser.

LASERSCAN

An instrument to measure mean fibre diameter and fibre diameter distribution by detection of shadows in a laser beam, brought about by causing snippets to be carried through the beam in a suitable liquid. 

Lot

Any number of bales of wool, of similar mass and dimensions, prepared for sale as a single parcel in accordance with accepted trade practices.

Mean

Arithmetic average; the mean of a set of values is calculated by dividing the sum of those values by the number of them. (For example, see Mean Fibre Diameter.)

where		= mean
		= the ith measurement made on the sample
		= is the number of items measured in the sample

Mean Fibre Diameter

The average thickness of a sample of fibres in micrometres. For wool, because individual fibres have different lengths, the mean diameter is weighted for the length. (Also see: Fibre Diameter Distribution, Fineness and Micron.) 

Medullation

The degree to which the centre of a wool fibre (the medulla) is hollow. Medullation is quantified in terms of the number of such fibres observed within a sample of fibres. 

MFD

See Mean Fibre Diameter Micrometre

A unit of length measurement equal to one-millionth of a metre; it is the unit of measurement for the fibre diameter of wool. It is commonly called a micron. The symbol ‘mm’ is used for micrometre.

Micron

Commonly used name for the unit of measurement of fibre diameter, correctly termed a micrometre (mm). 

Microtome

A mechanical guillotine consisting of two parallel, very thin sharp blades separated by a distance of 0.8 to 2.0 mm. The microtome is used to cut through a sample of wool top or wool sliver to obtain a sample of fibre snippets.

Minicore

A subsample obtained by small-diameter coring tubes to provide a representative snippet sample of sufficient mass.

Mounting Fluid

A clear fluid within which fibre snippets are dispersed prior to measurement by Projection Microscope.
The mounting fluid is spread on a glass slide and covered with a cover slip so as to ensure no air bubbles are retained within the fluid and the snippets are evenly dispersed throughout the fluid. 

OFDA

See Optical-based Fibre Diameter Analyser Optical-based Fibre Diameter Analyser.

Optical-based Fibre Diameter Analyser Optical-based Fibre Diameter Analyser

An instrument for measuring fibre diameter mean and distribution using an automated microscope and image analysis techniques. (Also referred to as OFDA.)

Precision

An indicator of the repeatability of a measurement; it is often expressed in terms of confidence limits. (Also see: Accuracy.)

Projection Microscope

An instrument for measuring fibre diameter mean and distribution. Magnified images of the profiles of short lengths (snippets) of fibre are projected on a screen and their widths measured by using a graduated scale. 

Raw Wool

Greasy wool; wool which has been scoured, carbonised, washed or solvent degreased; scoured skin wools; washed skin wools; and slipe wools. It consists of wool fibre together with variable amounts of impurities. 

SD

See Standard Deviation.

Sliver

See Wool Sliver Snippet

Very short pieces of fibre, typically around 0.8 to 2 mm long, which have been cut to measure fibre diameter and related properties. (Also see: Minicore, Microtome, Laserscan, OFDA and Projection Microscope.)

Standard Deviation

A measure of dispersion of individual results. Standard deviation is expressed in the units of measurement. (Also see: Variance and Coefficient of Variation.) 

Staple

A well-defined bundle of fibres which has been removed from a mass of greasy wool as a unit.

Staple length

The length of a staple projected along its axis obtained by measuring the staple without stretching or disturbing the crimp of the fibres. 

Top

See Wool Top or Wool Sliver

True Value

The absolute value of a characteristic; it is almost always unknown. Measurements of the characteristic are, in the absence of bias, normally distributed about the true value with a variance that is also unknown in a particular case. The mean of a set of measurements is the best estimate of the true value. (Also see: Accuracy.) 

Variance

The variance of a sample is the square of the standard deviation and is a measure of the distribution of values around the mean. It is expressed in the units of measurement squared. (Also see: Coefficient of Variation.) The variance of a sample may be calculated from:

where		= variance (standard deviation squared)
		= the ith measurement made on the sample
		= mean of the sample measurements
		= the number of items measured in the sample

Wool Base

The oven-dry mass of wool fibre free from all impurities, expressed as a percentage of the mass of the sample. 

Wool Sliver

A continuous strand of loosely assembled wool fibres which may contain variable amounts of vegetable matter and is approximately uniform in cross-sectional area and with none or very low levels of twist. This includes carded sliver, combed sliver, gilled sliver, top and roving. 

Wool Top

Sliver that forms part of the starting material for the worsted and certain other drawing systems, usually obtained by the process of combing, and characterised by the following properties: (a) A substantially parallel formation of the fibres, essentially free of vegetable matter. (b) The absence of fibres so short as to be uncontrolled in the preferred system of drawing. (c) A substantially homogeneous distribution throughout the sliver of fibres from each length group present.