Histograms measure the diameter of each fibre in a sample. Several aspects should be considered in deciding how to sample and how to use histograms. One is assessing how similar each fibre is to its immediate neighbour. This is what is shown in an individual histogram. Another aspect is how much variance there is among different areas of the fleece across the sheep’s body. This is shown by sampling from different points on the body of one sheep, with several histograms used in this assessment.

Histograms contain two types of information. One is a set of values, AFD, SD, CV, Spin Fineness, etc. that represent a summary of the measurements and some mathematical calculations using the measurements. The other information is presented in a visual format; a graph showing all of the measured diameters of the fibres in the sample.

When comparing histograms of samples at different points on the body (or just when comparing any histograms), note that the scale of the graphs on both the left and the bottom is not constant between histograms. The percentage or number of observations at each level, set out on the left side of the graph, may be changed from histogram to histogram to make a particular graph easier to interpret. This also happens along the bottom where the micron numbers are set out. Check this any time histograms are compared, if you like to use the visual graph in addition to the summary numbers.

If you want to compare samples from a number of sheep, it is important to sample all of them from the same area of their body. If the animals have much variation in their fleece across their bodies, moving even a few inches from the target spot can make a great deal of difference in the results and then the comparison is less useful. If the animals are very uniform, having the samples come from slightly different areas on their bodies will not impact the comparison as much.

If you are only going to use a single point for sampling, midside is recommended. The goal is to represent an average between the all parts of the usable fleece with just that one sample. If taken in the proper spot, a midside sample gives the best chance of obtaining a reasonable picture of the whole, usable fleece.

If garments are the desired end product for fleeces, or if you want to have them commercially process into knitting yarns, having a low Spin Fineness and high Comfort Factor (or Low % of Fibres over 30 Microns) at midside is an important consideration. Spin Fineness is a measure of how well the fleece will spin. 30 microns is the diameter at which most people will feel prickle or itch.  31 microns and up is considered coarse wool : The Sheep That Grow the Wool, American Wool Council, 1992.

If you have the ability to separate each fleece for use or processing based on the changes that occur in character across the body of the sheep, having a midside representative sample is probably less important.

Natural Fibre Centre in Canada and Yocom-McColl in the US can do histogram testing.