Kilt Do's and Don'ts

[Pour1Malt]

In almost all the paintings and photos I have seen of jackets worn with kilts of the same tartan, the jacket tartan is on the bias, that is, the tartan is diagonal, unlike the kilt. Which way, if either, is correct for jackets, or is or was customary, on the bias or horizontal and vertical?

jeekets and/arr waistcoats (neckties tae!) MUST have the tartan oan the bias...

arr else ya look like a sofa....