91/55445 DC : SEP 91被替代
AMENDMENT NO.1 TO BS 2497: PART 5: 1988 STANDARD REFERENCE ZERO FOR THE CALIBRATION OF PURE TONE AIR CONDUCTION AUDIOMETERS. PART 5: SPECIFICATION FOR A STANDARD REFERENCE ZERO USING AN ACOUSTIC COUPLER COMPLYING WITH BS 4668 (ISO 389: 1985/DAM 1)
出版：British Standards Institution
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