The critical difference CD_0.95 is used as tolerance of trueness verification in spark discharge atomic emission spectrometric analysis. When the measurement bias is not larger than the critical difference, it indicated that the measurement trueness is qualified. If more careful internal control means like type standardization are applied in the laboratory, the smaller critical difference of trueness should be adopted. For the process of spectral analysis without type standardization, CD_0.95 can be used for trueness verification. If the instrument is measured by type standardization for n₁ times, and the trueness verification is measured for n₂ times, the formula for critical difference is r·12n₁+12n₂. The critical difference value of trueness verification was 0.65r or 0.61r (r means repeatability limit) when the (n₁, n₂) combination was (3, 2) or (4, 2). After type standardization, if the operation time lasts for relatively long time (more than 1h), the critical difference for trueness verification is CD_0.95(R_w) which contained the time effect. The value was about CD_0.95/2. CD_0.95(R_w) of laboratory can be replaced by “warning limit”, i.e., 2S (standard deviation) in X-S monthly control chart. When the expanded uncertainty (U) of type standardization sample A and verification control sample B were considered (the coverage factor is k=2), the critical difference of trueness verification for sample B is r²12n₁+12n₂+U²_A+U²_B. Except spark discharge atomic emission spectrometry, any method which was corrected by type standardization can use the same formula of critical value as trueness verification within a short time.