# Digital calipers

Outside, inside, depth and step measurements, with contact geometry, setting, calibration and uncertainty limits.

Reviewed: 2026-11-01

Tags: inspection, instruments, dimensional-metrology

## What the instrument measures

A caliper’s outside, inside, depth and step contacts realize different measurements. Verify seating and contact geometry for the selected mode. [Mitutoyo, ABSOLUTE Digimatic Calipers](https://www.mitutoyo.com/products/small-tool-instruments-and-data-management/calipers/digimatic-calipers/absolute-digimatic-caliper/)

An **original acceptance example** illustrates the distinction. Suppose a drawing specifies 20.00 ±0.02 mm, so the limits are 19.98–20.02 mm. A corrected measurement of 20.01 mm with an independently evaluated expanded uncertainty of 0.03 mm has an interval of 19.98–20.04 mm. The indication lies within the drawing limits, but that interval extends beyond them. Apply the agreed decision rule; these hypothetical values neither characterize the named model nor prescribe a universal guard band.

| Measurement | Contact arrangement | Application question |
| --- | --- | --- |
| Outside | Opposing faces of the larger jaws | Are the intended external surfaces seated, without tilt or a burr? |
| Inside | Outward-facing contacts on the smaller jaws | Do the contacts reach the intended bore/slot surfaces rather than a chamfer? |
| Depth | Beam-end reference face and projecting depth bar | Is the reference seated and the bar touching the intended bottom? |
| Step | Rear step-measuring faces | Are both faces seated on the two intended parallel levels? |

NPL illustrates these arrangements in **Good Practice Guide 40, issue 2, updated September 2014**. Choose contacts from the drawing requirement. [NPL, Callipers and Micrometers, printed pages 11–12](https://eprintspublications.npl.co.uk/2043/1/mgpg40.pdf)

## Named model: read the complete specification

Mitutoyo catalog **E12047(2)** lists the metric **500-151-30** with a **0–150 mm** range and **0.01 mm** resolution. Its table distinguishes **partial surface contact error, E_MPE = ±0.02 mm**, from **shift error, S_MPE = ±0.04 mm**. These are maximum permissible error specifications, not an uncertainty statement for every workpiece measurement. The linked PDF's back page carries print code **2110(2)**; it does not present that code as a written calendar revision date. [Mitutoyo E12047(2), specifications](https://www.mitutoyo.com/webfoo/wp-content/uploads/E12047.pdf)

Mitutoyo's **2018** bulletin EDU-15003A explains that partial surface contact error applies to outside faces, while scale shift error applies to other contacts such as inside, depth and step, with zero established using the outside faces. Do not copy one attractive outside-measurement number into the capability statement for every measurement mode. The bulletin discusses ASME B89.1.14-2018; it is dated technical guidance, not an assertion that this edition governs every inspection contract. [Mitutoyo, Accuracy and Calibration of Calipers, page 1](https://www.mitutoyo.com.mx/webfoo/wp-content/uploads/15003A.pdf)

Confirm the exact model, contact geometry, range, output interface and environmental rating. The E12047 catalog distinguishes its IP67 coolant-proof instruments from other ABS Digimatic models and cautions that some aggressive fluids can degrade seals. A family name or digital display does not establish coolant resistance for every variant. [Mitutoyo E12047(2), product families](https://www.mitutoyo.com/webfoo/wp-content/uploads/E12047.pdf)

## Jaw alignment and force

The beam scale and contact line are offset. Slider tilt can therefore change the reading, with larger effects farther from the beam. Mitutoyo's Quick Guide discusses moving-jaw tilt and the resulting displacement, as well as small-hole error caused by the thickness and clearance of inside jaws. A stable reading at an unintended contact is still the wrong measurement. [Mitutoyo, Quick Guide to Precision Measuring Instruments, E11003(7), printed pages 20–21](https://www.mitutoyo.com/webfoo/wp-content/uploads/E11003-Quick-Guide.pdf)

Use light, repeatable contact and keep the measuring faces aligned with the required dimension. Do not squeeze a soft component until the display stops changing. Mitutoyo identifies excessive force as an error source and notes that ordinary calipers lack a constant-force device. [Mitutoyo Quick Guide, printed page 20](https://www.mitutoyo.com/webfoo/wp-content/uploads/E11003-Quick-Guide.pdf)

For outside measurements, support the part so that both jaws contact the intended surfaces; avoid balancing only on narrow jaw tips when deeper seating is possible. For an internal diameter, search for the diameter while maintaining the correct axial plane, rather than accepting a smaller chord. For a slot width, avoid skewing the contacts diagonally across the slot. The Quick Guide distinguishes seeking the maximum inside-diameter indication from the minimum groove-width indication. These techniques require the correct geometry; they are not permission to select the most favorable number from repeated readings. [Mitutoyo Quick Guide, printed page 21](https://www.mitutoyo.com/webfoo/wp-content/uploads/E11003-Quick-Guide.pdf)

## Zero, reference checks and calibration

A zero check asks whether the cleaned outside contacts indicate the reference origin when closed. An incremental zero can instead establish a comparison offset at another opening. Confirm which mode is active and record the reference when making comparative measurements. Zeroing a dirty instrument can hide contamination rather than correct it.

Mitutoyo's care guide calls for clean measuring faces, smooth slider motion and an origin setting after battery replacement for the illustrated Digimatic calipers. It also identifies separate outside, inside, depth and step contacts. [Mitutoyo, Check Points for Measuring Instruments, E12024, printed pages 8–9](https://www.mitutoyo.com/Images/E12024_Check_Points_for_Measuring_Instruments.pdf)

Calibration must investigate performance beyond closed-jaw zero: relevant lengths, contact positions and the modes actually used. A gauge-block check with outside jaws alone cannot establish inside-jaw or depth-bar performance. Select appropriate reference artifacts and an agreed procedure, and review results, corrections and restrictions rather than relying only on a sticker. Mitutoyo's calibration bulletin treats outside-face and other-contact errors separately for precisely this reason. [Mitutoyo EDU-15003A, calibration and error characteristics](https://www.mitutoyo.com.mx/webfoo/wp-content/uploads/15003A.pdf)

## Cleanliness, temperature and condition

Keep measuring faces and sliding surfaces free of chips and dirt. Inspect for contact damage and verify smooth movement. The E12024 care guide recommends removing contamination after use, arranging repair when damaged, and storing the illustrated calipers with the locking screw released and outside jaws slightly open. Follow the actual model's instructions for fluids, battery handling and storage. [Mitutoyo E12024, caliper care](https://www.mitutoyo.com/Images/E12024_Check_Points_for_Measuring_Instruments.pdf)

Temperature affects the instrument, reference and part. Do not measure a component still hot from machining and assume its indicated size represents the reference-temperature dimension. NPL identifies 20 °C as the dimensional reference temperature and discusses environmental effects on calipers. [NPL GPG40, printed page 25](https://eprintspublications.npl.co.uk/2043/1/mgpg40.pdf)

For reference artifacts, Starrett's gauge-block guidance also warns about hand heating, requires acclimation with the measuring instrument and workpiece, and distinguishes steel from materials such as aluminum or brass with different expansion coefficients. Equal ambient temperature does not make all materials expand identically. [Starrett, Use and Care of Precision Gage Blocks](https://www.starrett.com/products/gage-blocks-and-calibration-solutions/technical-data/use-and-care-of-precision-gage-blocks)

## Resolution and a defensible result

A 0.01 mm display increment is 10 µm. It describes the readout, not a universal ±10 µm measurement capability. Evaluate calibration/reference uncertainty, corrections, repeatability, resolution, alignment, force, contact condition and temperature for the actual task. NPL's caliper guidance distinguishes accuracy, precision and uncertainty and gives an application uncertainty example. [NPL GPG40, printed pages 26–29](https://eprintspublications.npl.co.uk/2043/1/mgpg40.pdf)

Record the dimension and location, measurement mode, instrument ID, reference checks, relevant corrections and conditions, result and applicable decision rule. If the contact geometry or evaluated uncertainty is unsuitable, choose a more appropriate method instead of deriving extra confidence from additional display digits.

## Related reference

[Inspection and quality documents](../../sourcing/documents/index.md)