…(A) sett stick was treasured in great houses as a visible standard for maintenance of the clan or family tartan. Surely, once it had been woven, a piece of the actual material would have served the same purpose more easily and effectively, in the unlikely event of the local weavers not being already familiar with the sett in all its details.
The colour-strips that accompany the Notes on the individual tartans correspond to the warp as it appears on the loom before the actual weaving is begun. For each colour-strip there is in the text a representative thread-count, and this by itself is sufficient for the weaver wishing to produce a tartan, but the colour strips give an immediate visual indication of the character of the design, and make it easy to identify any given tartan.
From The Setts of the Scottish Tartans (Stewart, pg. 4)
