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Measurement tools and calibration · Lesson 4 of 4

Measurement tools and calibration: defects, verification and case study

A bent hook, parallax, Abbe error, force and heat, the wrong tool or unit; a tape checked against a reference; what to do when a tool is out; a corner that is not square; and the record that goes with a reading.

You will be able to: Diagnose the common ways a reading goes wrong, work a tape-against-reference case, choose between re-zeroing, removal and calibration, and write a measurement record someone else can trust.

12 min · 11 slides · 10 questions

All lessons in this module
Slide 1 of 11

A bent or loose hook

A hook that is bent or forced out of shape moves the zero, so every reading from it is off by the same amount.

Test it: measure one known length hooked over an edge and again pushed against a stop; the two readings should match.

Stanley's patent describes a hook offset by about its own thickness so that both readings start from true zero.

Six common reading mistakes next to the right waySix pairs of small drawings, each with a correct panel marked with a green check and an incorrect panel marked with a red cross. One: a tape hook checked against a piece end versus a bent hook that moves the zero. Two: an eye straight over the scale versus an eye off to one side. Three: work held deep in the caliper jaws versus work at the tips of tilted jaws. Four: a micrometer closed with the ratchet on flat sheet versus forced on a bend. Five: a decimal reading recorded versus a gauge number only. Six: tool and part at the same temperature versus a warm hand on the tool frame.Six readings: right and wrongHook checkedHook bentzero movedEye square onEye off to a sideWork deep in jawsWork at the tipsRatchet, flat sheetForced on a bendforcedDecimal recordedGauge no. only.0276 inno decimalSame temperatureWarm hand on frame68 °F68 °Fwarmer

Six pairs of small drawings, each a correct panel with a green check and an incorrect panel with a red cross: a tape hook checked versus a bent hook, an eye straight over the scale versus off to one side, work held deep in the caliper jaws versus at tilted tips, a micrometer closed with the ratchet on flat sheet versus forced on a bend, a decimal reading versus a gauge number only, and tool and part at one temperature versus a warm hand on the tool.

Pairs drawn from the Mitutoyo and Starrett guidance and the Stanley hook patent cited in these lessons. Not to scale.

Sources

Videos for this lesson

What this video shows: Mitutoyo's own demonstration of the proper use of a digital caliper. Checked against the video's description.

Video: How To Use A Mitutoyo Digital Caliper by Mitutoyo America Corporation, on YouTube. Chosen from the video's published description.

Glossary

Abbe error
The error that appears when the scale and the line being measured are not on one axis, such as a caliper's tilted slider. It grows with the distance from the scale (Mitutoyo).
Fiducial line
The reference line on a micrometer sleeve or vernier that the scale is read against. Mitutoyo says to look directly at it when reading.
Measuring force
How hard a tool presses on the work. A micrometer ratchet limits it; a caliper has no constant-force device, so it depends on your hand (Mitutoyo).
Tool tolerance
The error a standard allows a measuring tool before it counts as out, such as the NIST Handbook 44 allowance for a metal tape. It is a benchmark for the tool, not the tolerance on a part.