How should you read the class labels in ISO 6789-1 Clause 7.2’s example?

Check the heading and both value entries

Start with the heading of the example in 7.2: it excludes Type II Classes B/C/E/F. Then read the entries describing the tool-side value. The second assigns the scale or display set value to A/D/G, while the third also assigns “nominal value” to A/D/G. The issue is not a different calculated percentage; it is the placement of the same adjustable classes in different value roles.

The third entry alone therefore does not establish that these tools should use the nominal value of a fixed-adjustment tool. Simply changing its letters to B/E would not resolve the issue either, because those classes would still conflict with the exclusions in the example’s heading.

Why the entry appears to have been carried over

Compare Clause 6.5, EXAMPLE 1 of ISO 6789:2003. The nominal-value line there refers to B/E. Its heading excludes only C/F, so fixed-adjustment tools remain within that example’s scope. This is a clue to a possible carryover of text, but similar wording alone cannot establish how the document was edited.

Next, look at 7.3 of the edition discussed here, where nominal set values for B/E are already included. Reading the fixed-adjustment case in that example fits the role of its value; there is no need to place it simultaneously in an example whose heading excludes it.

Finally, return to the general rules in 7.1: A/D/G use the scale or display set value, B/E use the nominal set value, and C/F use the lowest limit value or nominal pre-set value. This comparison confines our finding to the example’s class labeling. It does not change the definition of the target value or the relative-deviation formula.

Select the value and document your reading

In the calculation record, keep the standard edition, clause, original wording, and adopted reading together. Identify the tool class, the target value, and the source of that value. Preserve the original classes and short term in the questioned entry, then explain that the value was selected under the general rules. Do not present an edited version of the entry as an officially corrected provision.

For the actual calculation, establish the roles of target value X_t and measurement-device observed value X_o, then calculate each reading using this part’s formula. An example can help check the substitution steps, but a questionable class label should not redefine the tool’s classification. A record structured this way lets a reviewer distinguish a value-selection interpretation from an arithmetic problem.

This is our reading, not an official ISO corrigendum. ISO is revising Part 1 and Part 2 through committee drafts ISO/CD 6789-1.3 and ISO/CD 6789-2.3. We will update this page and recheck the issue when the revised standards are published.