A stripe is the most unforgiving cloth in upholstery, because it makes every line in the chair visible.
Stripes must run plumb - truly vertical - on the back and the arms, not parallel to the frame. Those two things sound the same and are not: the frame of this chair curves and tapers, so a stripe laid parallel to the frame edge would lean progressively as it rises and the whole back would look as though it were falling sideways.
So our upholsterers strike a vertical centre line on the chair itself, place the centre stripe on it, and work outward in both directions, letting the frame cut the stripes at whatever angle it happens to meet them. The stripe stays plumb and the frame's curve reads as curve.
The seat is then set out so the stripes align with those on the back - the same stripe running up the seat continues up the back panel behind it. It is a small thing, and it is the difference between a striped chair that looks designed and one that looks covered.