NVLAP LAB BULLETIN NUMBER: LB-115-2019 PAGE: 1 of 2

DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

National Voluntary Laboratory Accreditation Program

ISSUE DATE:

December 4, 2019

LAB BULLETIN NUMBER: LB-115-2019

LAP: Construction 

Materials Testing

SUBJECT: Clarification of Calibration Requirements for Nuclear Density Gauges

The purpose of this lab bulletin is to clarify how NVLAP interprets “calibration” in ASTM D6938, 

Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear 

Methods (Shallow Depth), and ASTM D7759/D7759M, Standard Guide for Nuclear Surface Moisture 

and Density Gauge Calibration.

ASTM D6938-17a section 8.1, on calibration says, “Gauge calibration shall be performed in accordance 

with Guides D7013 and D7759.” ASTM 7759/7759M-14 section 9, Density Systems Calibration, is 

obviously applicable. This section describes the process for determining the calibration constants or curve 

for a gauge. Section 10, Density Systems Verification, describes the process for determining if the 

existing calibration constants or curve are still applicable to the gauge. Is section 10 considered a 

calibration or is “verification” something less than a calibration?

JCGM 200 (VIM3): International Vocabulary of Metrology defines calibration as: 

operation that, under specified conditions, in a first step, establishes a relation between 

the quantity values with measurement uncertainties provided by measurement standards 

and corresponding indications with associated measurement uncertainties and, in a 

second step, uses this information to establish a relation for obtaining a measurement

result from an indication.

NOTE 1 A calibration may be expressed by a statement, calibration function, calibration 

diagram, calibration curve, or calibration table. In some cases, it may consist of an 

additive or multiplicative correction of the indication with associated measurement 

uncertainty.

NOTE 2 Calibration should not be confused with adjustment of a measuring system, 

often mistakenly called “self-calibration”, nor with verification of calibration.

NOTE 3 Often, the first step alone in the above definition is perceived as being 

calibration.

The process described in section 10 of ASTM D7759/7759M meets the definition of “calibration” as 

defined in VIM3. Section 9, Standardization, of ASTM D6938 is more consistent with “verification” as 

defined in ISO/IEC 17025:2017, General requirements for the competence of testing and calibration 

laboratories, section 3.8 or “intermediate check” as described in section 6.4.10 of ISO/IEC 17025.
NVLAP LAB BULLETIN NUMBER: LB-115-2019 PAGE: 2 of 2

Either process, calibration, section 9, or verification, section 10, as described in ASTM D7759/7759M 

must meet NVLAP traceability requirements defined in NIST Handbook 150 Annex B, Implementation 

of Traceability Policy in Accredited Laboratories. Sections 9.6 and 10.2 of ASTM D7759/7759M apply 

only if in compliance with Annex B of Handbook 150.

This clarification is for the purposes of NVLAP assessment and accreditation. Other specifiers may have 

requirements that differ.

Questions should be directed to Timothy Rasinski, program manager, at 301-975-6697 or 

timothy.rasinski@nist.gov.