Also known as: calibration block, IIW block, V1 block, V2 block, step wedge, reference standard.
Why they matter
Every ultrasonic result is relative to a calibration; if the block is wrong or unrecorded the result cannot be reproduced. Codes therefore specify block material, acoustic properties and reflector sizes, and auditors check the block certificates.
Reference blocks in AMPS
Blocks are equipment in AMPS: each has its certificate on the equipment page with a due date flag, and the report template can carry the block serial number as a filled field.