# Reference block (calibration block)

> A reference block is a machined piece of known material and geometry (IIW V1 and V2 blocks, step wedges, blocks with side-drilled or flat-bottom holes, notched blocks) used to calibrate range and sensitivity of NDT instruments and to demonstrate a technique.

- Source: https://amps.global/glossary/reference-block/
- Type: Glossary
- Published: 2026-09-05
- Tags: quality, calibration, ultrasonic testing

## Key facts

- Ultrasonic range and velocity calibration: IIW V1 (ISO 2400) and V2 (ISO 7963) blocks; thickness: step wedges
- Sensitivity and DAC/TCG: blocks with side-drilled holes to ASME V Article 4 or ISO 17640
- Blocks are serial-numbered, certified for material and dimensions, and periodically re-verified
- The block used is recorded on the report for repeatability

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.

## Related pages

- [Ultrasonic testing (UT)](https://amps.global/glossary/ultrasonic-testing/)
- [Calibration certificate](https://amps.global/glossary/calibration-certificate/)
- [Free UT linearity tool (ASME V)](https://amps.global/ndt-tools/linearity/)

## Sources

- [ASME Boiler and Pressure Vessel Code](https://www.asme.org/codes-standards/bpvc-standards)
- [ISO - International Organization for Standardization](https://www.iso.org/)