Black Watch to the stripe: checking my math

[Barb T]

An asymmetric tartan is one that doesn't have a mirror image repeat. The Black Watch is an ABACABAC type tartan, and the "C" block is a pivot (mirror) block. You can see below that the repeat is exactly the same going left or right from the "C". That makes it symmetrical. Neither A nor B are pivots, but that doesn't make the tartan asymmetrical. As long as there is at least one pivot, the tartan is symmetrical.

ABA C ABA C ABA C ABA C

A tartan that is an ABCABCABC type tartan has no pivots:

A BC A BC A BC
or
AB C AB C AB C
or
A B CA B CA B CA

Neither the A nor the B nor the C is a pivot, because the sett isn't the same going each way from the single letter in the examples above.

[Huoliuhi]

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