How do I know if my sitting posture is right? I keep adjusting my back and legs and I don't know what 'correct' means.

answered

The short answer: the classical tradition has one test and it is not in a mirror — a posture is right when the breath stays even and unforced in it. Zhiyi’s five adjustments states the rule as a pair of negations: not slack, not strained (不宽不急). Everything else — the straight back, the level head, the hands in the lap — is the means to that one end, and the archive’s own instruction says it outright: do not stretch upward like pulling a scallion; the spine is straight enough when breathing is easiest in it.

The classical anchor

The sitting-protocol page holds the full classical sequence; for this question, two facts matter:

• The test is functional, not visual. The Xiao zhiguan adjusts the body before the breath — but only so the breath can then be adjusted; the body-check is never free-standing. A posture that looks canonical in the mirror and produces strained breathing is wrong, by the tradition’s own standard.
• The founding image is not a heroic posture. The Zhuangzi’s opening sitting scene is a master leaning on his armrest (隐机而坐) — the book that supplies half the tradition’s vocabulary begins with a lean, not a lotus. The site’s cross-legged question draws the practical consequence: posture is a tool, not an entry requirement.

The archive’s concrete checklist

The archive chapter on lotus posture gives the most detailed symptom-based checklist the site has recorded, and it is useful precisely because every item is anchored to a symptom rather than a shape:

• The hips come first. Pad the rear third of the cushion so the hips sit above the knees — the pelvis tilts slightly forward in single lotus and long sitting becomes impossible; the pad is the fix.
• The spine: straight but not pulled. 腰板要挺直，但不要挺得自己不舒服 — straight, but not to the point of discomfort. The explicit negative: do not stretch upward like pulling a scallion. The test: breathe easily.
• The head: slightly forward. Both looking up and tucking too far down compress the windpipe and make breathing harder — the head stops where breathing is most open.
• The eyes: half-open, unfocused, at about 1.5 meters — closed eyes feed wandering thoughts in beginners; the gaze is a resting one, not a stare.
• The mouth: closed; the teeth: lightly touching — clenched teeth bring gum inflammation; a hanging jaw slackens the muscles and stimulates the salivary glands.
• The tongue: lightly on the palate — touching, not curled back.
• The hands: the mudra resting in front of the lower belly — right fingers on left, thumbs joined, sitting there without tension.
• The single-lotus tilt is the one posture the archive singles out as a known trap: it is fine as preparation, but it will not hold a long session, and forcing it longer than it holds is how injuries start.

The error signal that overrides everything

The archive’s most important rule for this question is the discrimination between mental and physical trouble, recorded on the EXP-031 page: mental causes (restlessness, lust, irritation) are the targets of sitting — keep sitting through them; physical pain that keeps intensifying into labored breathing means the posture has a problem, and the problem must be found and removed — otherwise, the archive says plainly, the body breaks. The site’s leg-numbness-pain pattern page states the modern form of the same rule: pain that worsens across sessions is a body signal, not a milestone.

The asymmetry, stated once: the tradition gives you a symptom checklist and a breath test, not a ruler — and that is not a deficiency. The progress question explains why: what can be self-checked is the process (breath rate, session length, discomfort trends), not the stage. Posture is process, not stage — so it can be checked, and the check is the breath.