· Linear units (length/pressure/force/torque/mass/roughness) are exact conversions

· Hardness uses empirical reference values (ref. GB/T 1172, ASTM E140); may deviate for different materials - estimate only

· Ra and Rz have no exact relationship; this tool does not convert between them

· PPM is the total two-sided defect rate (above upper limit + below lower limit)

· Checking "1.5σ shift" uses the Six Sigma long-term convention: Z=6 → 3.4 PPM

· Unchecked = short-term (no shift, symmetrical): Z=6 → approx 0.002 PPM

· Corresponding Cpk = Z ÷ 3 (valid for two-sided specs, no offset)

· AP (Action Priority) follows the AIAG-VDA FMEA handbook (1st ed. 2019), replacing the old RPN

· AP prioritizes severity: when S≥9 most combinations are rated "High"

· RPN = S×O×D is shown for reference only; the new handbook no longer decides by RPN threshold

· WC (worst-case): tolerances added in absolute value, guarantees 100% conformance but conservative - suited to tight-fit, low-volume chains

· RSS (root-sum-square): square-root of sum of squared tolerances, assumes independent near-normal dimensions (about ±3σ) - suited to high-volume statistical control

· Direction: default "+" adds; use "-" to indicate the dimension reduces the stack result (e.g. shaft clearance)