Section 31.12 - Proof of compliance(a) Each requirement of this subpart must be met at each weight within the range of loading conditions for which certification is requested. This must be shown by-(1) Tests upon a balloon of the type for which certification is requested or by calculations based on, and equal in accuracy to, the results of testing; and(2) Systematic investigation of each weight if compliance cannot be reasonably inferred from the weights investigated.(b) Except as provided in § 31.17(b) , allowable weight tolerances during flight testing are + 5 percent and -10 percent.Amdt. 31-4, 45 FR 60179, Sept. 11, 1980