DAY 22 — CALIBRATION CURVE

What is a calibration curve?

A calibration curve expresses the relation between indication and the corresponding measured quantity value

What VIM reference is shown for calibration curve?

VIM 4.31

What two quantities are connected by a calibration curve?

Indication and measured quantity value

Why does a calibration curve matter?

It helps us understand instrument behavior across a range

What effects can a calibration curve reveal?

Offset scale-factor effects nonlinearity and range behavior

What determines how a calibration curve is developed and evaluated?

The applicable method

What should be done when starting with calibration data?

Collect relevant calibration points across the applicable range

What should be used when developing a calibration curve?

The right method procedure and requirements such as manufacturer customer and regulatory requirements

What relationship does a calibration curve show?

The relationship between instrument indication and measured quantity value

Is a calibration curve itself a measurement result?

No it is a relationship not a measurement result by itself

What VIM reference is shown for the relationship between indication and measured quantity value?

VIM 4.31

What is a common linear calibration model?

Y = a + bX

What does a represent in the linear calibration model?

a represents the intercept

What does b represent in the linear calibration model?

b represents the slope

What does the actual calibration model depend on?

The measurement method and data

What are possible calibration curve models shown?

Linear quadratic and other models such as power and exponential

What is the linear model shown?

Y = a + bX

What is the quadratic model shown?

Y = a + bX + cX²

What warning is given about assuming linearity?

Do not assume linearity without evidence or an applicable method

What is the illustrative calibration curve model in the example?

Q = a + bI

What value is given for a in the example?

a = −0.20 °C

What value is given for b in the example?

b = 1.004

What value is given for I in the example?

I = 50.00 °C

What equation is shown when the example values are substituted?

Q = −0.20 + (1.004 × 50.00)

What is the calculated Q in the illustrative example?

Q = 50.00 °C

What does the infographic say about the numerical calibration example?

It is an illustrative example and not actual calibration data

What can the intercept represent?

The intercept can represent an offset in the relationship

What does the slope describe?

The slope describes the scale relationship

How should slope and intercept values be interpreted?

They must be interpreted using the applicable method and calibration data

Why does model adequacy matter?

A curve may look good visually but still be inappropriate

What questions should be asked about model adequacy?

Does the model represent the data is it appropriate for the intended use what is the range of validity and what about residuals and assumptions

What should be checked when evaluating a calibration model?

Whether the model represents the data

What should be checked about intended use?

Whether the model is appropriate for the intended use

What should be checked about validity?

The range of validity

What should be considered regarding residuals and assumptions?

Residuals and assumptions should be considered

How does a calibration curve differ from a measurement result?

A calibration curve is a relationship while a measurement result is a value together with uncertainty information and other relevant details

What does a calibration curve show?

How indication relates to measured quantity value

What does a measurement result require?

Uncertainty information and other relevant details

What is the difference between a calibration curve and a calibration diagram?

The calibration curve shows a one-to-one relation between indication and value while the calibration diagram shows a one-to-many relation with uncertainty representation

What VIM references are shown for the calibration curve and calibration diagram?

VIM 4.30–4.31

What does the calibration curve diagram represent?

A one-to-one relation between indication and measured quantity value

What does the calibration diagram represent?

A one-to-many relation with uncertainty representation

What is the first technician red flag?

Assuming every curve is linear

What is another technician red flag concerning range?

Using a curve outside its applicable range

What is the warning about an old calibration curve?

Do not copy an old curve without checking current data

What model-related red flag is identified?

Ignoring model adequacy

What should not be treated as the complete measurement result?

The curve itself should not be treated as the complete measurement result

What should a calibrator ask instead of only asking whether the graph looks good?

Ask whether the model represents the data whether it is appropriate for the intended use and what the limits and uncertainty are

What question is posed about the graph looking good?

Does my graph look good?

What additional question should be asked about the model?

Does my model represent the data?

What should be checked about intended use?

Whether the model is appropriate for the intended use

What should be checked about limits and uncertainty?

The limits and uncertainty should be considered

What technical challenge is presented about VIM3 and calibration curves?

VIM3 says a calibration curve does not provide a measurement result

What important information is missing if a calibration curve does not provide a measurement result?

The measurement result information is missing

What witty challenge is presented?

If your calibration curve looks perfect but has no uncertainty information is it calibration or just a pretty graph?

What global reference is given for calibration diagram?

VIM3 — JCGM 200:2012 reference 4.30 Calibration diagram

What global reference is given for calibration curve?

VIM3 — JCGM 200:2012 reference 4.31 Calibration curve

What VIM reference is given for calibration?

VIM3 — JCGM 200:2012 reference 2.39 Calibration

What other reference is listed?

NIST Engineering Statistics Handbook — Instrument calibration over a regime

What procedural reference is listed?

Applicable calibration method / SOP

What does the infographic say about calibration data points?

Relevant calibration points should be collected across the applicable range

What does the infographic say about the relationship model?

The calibration data are used to establish a relationship between reference value and UUT indication

What is one effect a calibration curve can reveal besides offset?

Scale-factor effects

What is another effect a calibration curve can reveal besides scale-factor effects?

Nonlinearity

What range-related behavior can a calibration curve reveal?

Range behavior

Why should linearity not be assumed automatically?

Because the applicable evidence or method must support the model

What can happen if a visually good curve is inappropriate?

The curve may still be inappropriate despite looking good visually

What should be considered before using a calibration curve for its intended purpose?

Whether the model represents the data whether it is appropriate for the intended use and its range of validity

What should be considered about residuals when assessing model adequacy?

Residuals and assumptions should be considered