Dial indicator calibration: procedure, standards and how often to calibrate

What a dial indicator calibration checks

A calibration compares the indicator's readings with known displacements from a traceable reference. It records the error at each test point together with the uncertainty of the check. Comparing those errors with a maximum permissible error (MPE) and recording a pass or fail is a verification, and most certificates carry both.

The German calibration guideline for dial indicators, DKD-R 4-3 Blatt 11.1, published by PTB, lists five characteristics to determine. The table sets them out.

• Calibration vs verification

The standards: ISO 463, ISO 9493 and ASME B89.1.10M

ISO 463:2006 sets the design and metrological characteristics of mechanical dial gauges, the plunger-type instruments usually called dial indicators in the US. The movement of the plunger is magnified by a mechanism and shown by a pointer on a circular scale. The standard gives MPE values and limits for a number of metrological characteristics, has a clause on measuring forces and covers calibration in an informative annex. It has two corrigenda, from 2007 and 2009, and ISO last confirmed it in 2020.

A revision is under way. ISO/DIS 463, a draft titled for indicators in general, will replace both ISO 463:2006 and ISO 13102:2012, the standard for electronic digital indicator gauges. Voting on the draft closed in March 2026. Until the new edition is published, ISO 463:2006 and ISO 13102:2012 are the current standards.

ISO 9493:2010 covers dial test indicators of the lever type, in which a pivoting stylus drives the pointer. It names three common types by where the dial sits: S for standard, H for horizontal and V for vertical. The indicator has to measure with the stylus moved either way from rest. ISO last confirmed it in 2021.

ASME B89.1.10M-2001, reaffirmed in 2021, is the US standard for dial indicators used to measure a linear dimension or a variation from a reference dimension.

Equipment and conditions

There are two ways to supply known displacements. A dial indicator calibrator moves the plunger through set distances with a micrometer head or a length measuring system. Steel gauge blocks wrung in a staircase on a glass flat or a surface plate give fixed steps. The calibration procedure DI-010 of CEM, the Spanish national metrology institute, describes both.

• A calibrator whose range covers the indicator's range. CEM recommends a calibrator uncertainty of no more than half the indicator's scale interval.
• Or steel gauge blocks used one at a time rather than in stacks. For a scale interval of 0.001 mm or coarser, CEM accepts grades 0, 1, 2 or K.
• A rigid stand that holds the indicator square to the reference.
• A stable room. The DKD guideline asks for 20 °C ± 1 K as a minimum. CEM accepts (20 ± 3) °C for a scale interval of 0.001 mm or coarser, once the equipment has spent 24 hours in the room.
• Gloves, so that handling does not warm the blocks or the stand. CEM waits at least 15 minutes after setting up before it starts.

• Gauge block calibration

Test points across the range, in both directions

Start at zero and read the indicator at points spread over the whole range with the plunger moving in. Then come back through the same points with the plunger moving out, without setting the zero again. Approach each point from one direction only, so that the pointer lands on the graduation without going back. The error at each point is the reading minus the reference displacement.

Choose points that leave the pointer at different places on the dial. An error that repeats with each turn of the pointer only shows when the test points fall at different angles. The two national guidelines set the minimums in the table.

Hysteresis, repeatability and the short-span error

Hysteresis is the difference between the readings at the same point with the plunger moving in and moving out. An indicator that reads both rising and falling values carries its hysteresis into the result.

Repeatability is the scatter of repeated readings at one point under the same conditions, taken by moving the plunger away and back. The DKD guideline asks for at least five readings. For indicators with a scale interval of 0.001 mm or coarser, CEM takes at least six readings at each end of the range and pools the two standard deviations into one figure with at least ten degrees of freedom.

The short-span error catches a local fault that wide test steps would miss. The DKD guideline adds it when the steps are wider than ten scale divisions. It matters most for comparison work, where the indicator is set to zero on a master and reads only small differences over a short part of its range.

Measuring force and mechanical condition

Check the indicator before you calibrate it. The plunger should move smoothly over its whole travel with a steady measuring force, the pointer should not stick and the dial should be easy to read. CEM's procedure does not go on until a fault found here is repaired. The DKD guideline adds that the repeatability has to be clearly smaller than the indicator's error limits before a calibration is worth doing.

ISO 463 and ISO 9493 each have a clause on measuring forces (clause 5.3 in both). When the force matters for your parts, check it with a force gauge against the requirement in the standard or the maker's specification.

Dial test indicators (lever type)

A dial test indicator reads the movement of a pivoting stylus. ISO 9493 says it indicates displacement at right angles to the stylus, and a reading taken at any other angle needs a correction, with notes on use in the standard's Annex D. In practice, set the stylus as close to parallel with the surface as you can. At an angle the indicator reads more than the real movement.

Calibrate a dial test indicator in both measuring directions, since it has to measure with the stylus moved either way. The DKD guideline for dial test indicators, DKD-R 4-3 Blatt 11.3, reads it in steps of five scale divisions in each direction, with the reference moving at right angles to the stylus. Where the errors at two successive points differ by more than half a division, it adds a short-span check there in ten steps of one division.

Record the position of the indicator and of the stylus during the calibration. The DKD guideline asks for both, because the errors can change with position.

As-found and as-left readings

Record the readings at each point before anything is cleaned, adjusted or repaired. Those are the as-found readings, and they show how the indicator was measuring while it was in use. Note where the zero was set, because the DKD guideline asks for the zero position on the record. After a repair or a cleaning of the mechanism, repeat the calibration and record the as-left readings.

When an as-found error is outside the limit, ISO 9001 clause 7.1.5.2 asks you to determine whether earlier results were adversely affected and to act where needed. Look at the size and direction of the error over the part of the range the indicator was used in. An indicator set to zero on a master and used for small differences is affected only by the error over that span.

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• As-found and as-left worksheet

How often to calibrate a dial indicator

No standard sets one interval. ISO 9001 asks for calibration or verification at specified intervals, or before use. ILAC-G24 and OIML D 10 (2022 edition) list the factors to weigh, such as wear, how much and how hard the equipment is used, its environment and its calibration history.

CEM's procedure DI-010 gives guide values for indicators in normal use in a metrology room: 6 to 24 months for a scale interval of 0.001 mm or coarser, and 6 to 12 months for finer ones. For heavy use or a harsher place such as the shop floor, it advises a shorter interval, even below those ranges. The choice stays with the user.

Between calibrations, check the indicator against a gauge block or a master at the size you use, and check it again after a drop. ISO/IEC 17025:2017 clause 6.4.10 calls these intermediate checks and expects a procedure for them where they are needed to keep confidence in the equipment.

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TUR and resolution

The test uncertainty ratio (TUR) compares the limit being checked with the expanded uncertainty of the check. For a symmetric limit of ±T and an expanded uncertainty U at about 95 percent coverage, TUR = T / U. ANSI/NCSL Z540.3 accepts a TUR of at least 4:1 where the probability of a false accept cannot practicably be estimated. Ask your lab which decision rule its pass or fail statements follow.

Resolution adds uncertainty because the reading is rounded to its last step. The GUM (JCGM 100:2008, F.2.2.1) gives the step divided by √12 as its standard uncertainty, about 0.29 times the step. For a digital indicator that reads to 0.001 mm, that is about 0.29 µm. On a dial, the reading uncertainty depends on how the reading is taken. CEM reads to the nearest graduation and so uses the scale interval divided by √12, and the DKD guideline lists the reading uncertainty in its budget.

• TUR and TAR calculator
• Resolution uncertainty calculator
• How to build a measurement uncertainty budget

What the certificate and record should show

Whether the work is done in-house or by a lab, the record of each calibration should let someone else check it later.

• The indicator's ID, type, range and scale interval or digital step.
• The calibrator or gauge blocks used, with their certificate numbers and due dates.
• The position of the indicator during the calibration and where the zero was set. For a dial test indicator, the position of the stylus as well.
• The errors at each point moving in and moving out, the hysteresis and the repeatability, as found and as left.
• The temperature, the uncertainty of the calibration and the decision rule behind any pass or fail statement.
• The date, the person or lab, and the next due date.

• Calibration certificate requirements
• Calibration certificate template

How Axiospec helps with dial indicators

Axiospec is calibration management software. It does not calibrate an indicator. On an in-house calibration, a final reading outside its tolerance sets the result to Fail, and recording a pass anyway takes a written reason. The tolerance, the decision rule and the interval stay with you or your lab. Axiospec keeps the record of each calibration with the indicator.

When you log a calibration, each test point gets its own row with the nominal value, the as-found and as-left readings and the tolerance. A point can be marked up-scale or down-scale, so the in and out passes sit in one record. Each reading shows whether it is in tolerance or by how much it is out. The calibrator or gauge block set is picked from the register as the reference standard, with its own certificate and due date on its record.

A calibration logged as Fail puts the indicator in quarantine, and the failed record asks for the out-of-tolerance impact. The free plan covers up to 50 active instruments. A new workspace starts with a 45-day trial of Professional, with room for 1,500 active instruments and no credit card. We load your existing records for you at no charge on every plan.

• Free as-found and as-left worksheet
• Free calibration log template
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