My first kilt begins!

[Grizzled Ian]

A symmetrical tartan has the same order of the colours and threadcount both across and up and down, and that is what I see in your piece of Grant. The weaving process, however, in mills both great and small, is rarely able to achieve exactly the same measure in the sett repeat in both warp and weft. So a symmetric tartan may not meet a strict geometric understanding of symmetry - but to a man on a galloping horse it's a symmetric tartan, OK?

BTW, your tape measure and your straight edge are laid down on different elements of the tartan, and neither one is a full sett repeat. The tape only measures the two wider red stripes (0" to 2 3/4") while the wooden ruler covers the two wider black stripes (0" to 4 1/4"); but note that the tape from 2 3/4" to 7" covers the same as the ruler covers; and that the full sett repeat is under the tape from 0" to 7".

But now it's time to get stuck into working out your preferred pleating option. Depending on how much each pleat narrows from hip to waist, you might have two or four stripes to choose from to avoid spear-pointing. Have fun!