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Guard band: the measurement did not move and the three rules disagreed

Type a measured value, its uncertainty and the limit. On a value of 100 against a limit of 100, three declared rules return no statement, a fail and a pass, and the measurement never moved.

Live result

At a measured value of 100 against the upper limit 100, the three declared rules return no statement, fail, and pass.
At a measured value of 100 against the upper limit 100, the three declared rules return no statement, fail, and pass.

Try a scenario

The measurement and its three readings

Limit kind

1.00
2.00

This is the one control the chart and sweep move. The measurement, limit, direction, and guard share stay fixed.

One measurement against three acceptance limitsThe measured value is 100 with uncertainty 2. The stated, inward, and outward limits are 100, 98, and 102. Their answers are no statement, fail, and pass.Plain comparisonno statement100measurementacceptance limitInward limitfail98Outward limitpass102

Tracked answer

Plain comparison

Acceptance limit

100

no statement

Inward limit

Acceptance limit

98

fail

Outward limit

Acceptance limit

102

pass

Measured value: 100

Uncertainty

It does not check the values in between.

How the answer sits across the values sampledA rail of the 9 values sampled, from 0.00 to 4.00 in steps of 0.50. Across the values sampled, the three answers together stays no statement / fail / pass from 0.50 to 4.00, the highest value sampled. The nearest value where it changes is 0.00, where it becomes no statement / pass / pass.first change0.002.00on the page

Across the values sampled, the three answers together stays no statement / fail / pass from 0.50 to 4.00, the highest value sampled. The nearest value where it changes is 0.00, where it becomes no statement / pass / pass.

Across the values sampled, the three answers together stays no statement / fail / pass from 0.50 to 4.00, the highest value sampled. The nearest value where it changes is 0.00, where it becomes no statement / pass / pass.
The answerno statement / fail / pass
Values sampled0.00 to 4.00, 9 values, step 0.50
Holds from0.50
Holds to4.00, highest sampled
Nearest value that changes it0.00
The answer thereno statement / pass / pass

What an unchanged region does and does not prove is set out in a short lesson.

The sweep samples only the values you entered. Between samples the answer is not checked, so read the boundary as observed, not proven.

First checked change for each rule

Plain comparisonno change in range
Inward limit0.5 · fail
Outward limitno change in range

Only uncertainty moves. Each first change belongs to the checked grid, so it is not an interpolated crossing.

It describes what each declared rule returns for the typed numbers, without choosing a rule, issuing conformity, or grading any verdict.

Here is the maths

The formula, in words

Multiply uncertainty by the typed guard share. For an upper limit, subtract that guard for the inward limit and add it for the outward limit. For a lower limit, reverse those two shifts. The point rule gives no statement at exact equality. The shifted rules include equality.

G=g×uG=g\times u
where GG is the guard, gg the guard share, and uu the uncertainty.
Li=L−GL_i=L-G
where LiL_i is the inward upper limit and LL the stated limit.
Lo=L+GL_o=L+G
where LoL_o is the outward upper limit.

A worked example

  1. The upper limit is 100, the measured value is 100, uncertainty is 2, and guard share is 1.
  2. The inward acceptance limit is 100−1×2=98100 - 1 \times 2 = 98, so the measured value fails that declared rule.
  3. The outward acceptance limit is 100+1×2=102100 + 1 \times 2 = 102, so the measured value passes that declared rule.
  4. The point comparison meets the limit exactly and returns no statement.

What this does not model

It does not choose the rule a specification requires, interpret a specification, estimate measurement uncertainty, grade a rule, or issue a conformity statement.

What the sweep holds fixed

Only uncertainty moves. The measured value, specification limit, limit kind, and guard share remain fixed at the values on the page.

Source anchors

The sources describe decision rules and conformity statements. This page does not reproduce their text.

The whole record prints. Your browser can save it as a PDF instead of printing it.

No governing rule is selected and no conformity statement is issued here. The source explains why the decision rule used for a conformity statement needs to be identified.

Related

Declared rule comparison record

Guard band: the measurement did not move and the three rules disagreed

Accepted inputs

Measured value
100
Specification limit
100
Limit kind
Upper
Guard share
1
Uncertainty
2

Tracked answer

Plain comparison
100, no statement
Inward limit
98, fail
Outward limit
102, pass

Record fields

Calculation version
1.0.0
Boundary
It describes what each declared rule returns for the typed numbers, without choosing a rule, issuing conformity, or grading any verdict.
Permanent refusal
No governing rule is selected and no conformity statement is issued here. The source explains why the decision rule used for a conformity statement needs to be identified.
Sources
ILAC, G8:09/2019 guidance listing. ISO, public description of ISO/IEC 17025:2017

No governing rule is selected and no conformity statement is issued here. The source explains why the decision rule used for a conformity statement needs to be identified.

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