Metrology for Engineering Technicians

Principles, Measurement Systems, and Data Analysis

Chapter 5 of 8

Chapter 5: Dial Gauges and Indicators

5.1 Introduction

Dial gauges (also called dial indicators) are comparative measuring instruments. Unlike calipers and micrometers, dial gauges do not directly report an absolute dimension. Instead, they measure deviation from a reference value. In manufacturing and quality control, this makes dial gauges indispensable for inspection, alignment, flatness checks, parallelism, and runout measurements.

This chapter introduces dial gauges as part of a measurement system, typically used with surface plates, comparator stands, magnetic bases, and gage blocks. Students will learn how to properly mount, zero, read, and interpret dial gauge measurements in both inch and metric systems.

5.2 What Dial Gauges Measure

Dial gauges are used to evaluate:

Dial gauges answer the question: How much different is this feature from what it should be?

They are not intended to replace calipers or micrometers for absolute measurement.

5.3 Major Components of a Dial Gauge

A typical dial gauge consists of:

Some dial gauges include a turns counter, while others require the operator to track revolutions manually.

Labeled diagram of a dial indicator A dial indicator drawn from the front. A large round dial face is graduated from 0 at the top with marks every ten divisions: 10, 20, 30, 40, 50 at the bottom, then 60, 70, 80, and 90 back up to zero. A long needle points up and to the right. A small inner dial near the center is the turns counter. The outer ring is the bezel, which rotates to set zero. Below the dial, the stem extends downward to the plunger and the rounded contact tip. Labels with arrows identify the bezel, dial face, pointer, turns counter, stem or shank, plunger, and contact tip. 0 10 20 30 40 50 60 70 80 90 Bezel (rotate to zero) Pointer (needle) Dial face Turns counter Stem (shank) Plunger Contact tip
Figure 5.1. Major components of a dial indicator. The small inner dial is the turns counter — it records how many full revolutions the needle has made. (Figure redrawn for this edition.)

5.4 Dial Gauge Types and Discrimination

Common dial gauges used in MET 135 include:

Inch Dial Gauges

Metric Dial Gauges

The discrimination is always printed on the dial face and must be identified before taking measurements.

5.5 Mounting Dial Gauges

Dial gauges must be mounted rigidly and perfectly vertical for height measurements.

Mounting methods include:

Before measurement:

Improper mounting introduces cosine error and invalidates measurements.

Dial indicator mounted on a comparator stand over a surface plate A comparator stand with a vertical column rises from a heavy base sitting on a flat surface plate. An arm extends from the column and holds a dial indicator vertically. The indicator's plunger points straight down and its contact tip rests on a gage block stack placed on the surface plate. Labels identify the dial indicator, column, plunger, gage block stack, and surface plate. Dial indicator Column Plunger (stylus) Gage block stack Surface plate
Figure 5.2. A dial indicator mounted on a comparator stand, zeroed on a gage block stack over a clean surface plate. (Figure redrawn for this edition.)

5.6 Zeroing a Dial Gauge Using Gage Blocks

Dial gauges are zeroed using gage block stacks, not the surface plate.

Zeroing procedure:

  1. Stack gage blocks to the nominal dimension
  2. Wring blocks together
  3. Bring the dial gauge down until the pointer makes 1–3 full rotations
  4. Rotate the bezel to align zero with the pointer
  5. Lock the bezel
  6. Record the turns counter (or number of rotations)

The gauge is intentionally preloaded so it can measure values both above and below the specification.

5.7 Reading Dial Gauges

Direction of Needle Movement

Reading Steps

  1. Determine the number of full rotations (from turns counter or tracking)
  2. Read the main dial
  3. Multiply by the discrimination
  4. Apply sign (+ or −) based on direction

Measurement = ±[(full revolutions × range per revolution) + (dial divisions × discrimination)]

Note: On a typical 0.001 in gauge with 100 divisions, one full revolution equals 100 × 0.001 = 0.100 in. On a typical 0.01 mm gauge, one revolution equals 1 mm. See Note 4 in Notes & Clarifications.

5.8 Example Dial Gauge Reading

Example (Solved)

Gauge: 0.001 in discrimination (0.100 in per revolution)
Turns counter = 1 revolution
Main dial reading = 23 divisions (clockwise)

Measurement = (1 × 0.100) + (23 × 0.001) = +0.123 in relative to the reference

(Corrected in this edition: full revolutions are worth 0.100 in each on this gauge. The original printing omitted the revolution and reported +0.023 in.)

Try It: Dial Gauge Reading Calculator

Enter what you see on the gauge; the tool applies the formula from Section 5.7.

5.9 Application Examples

Dial gauges are used in industry to:

Dial gauges simulate real inspection stations used in manufacturing quality control.

5.10 Chapter Summary — Study Points

Chapter 5 Exercises

Each exercise includes a worked example followed by a student practice problem. Unless stated otherwise, inch gauges have 0.001 in discrimination with 0.100 in per revolution, and metric gauges have 0.01 mm discrimination with 1 mm per revolution. Needle motion is clockwise unless noted.

Exercise 1: Identifying Discrimination

Example (Solved)

Dial face marking: 0.001 in
Each small division = 0.001 in

Student Practice

A metric dial gauge is marked 0.01 mm. What is the value of one small division?

Show answer

0.01 mm

Exercise 2: Reading an Inch Dial Gauge (No Turns Counter)

Example (Solved)

Needle moves clockwise 18 divisions (less than one revolution).
Measurement = +0.018 in

Student Practice

Needle moves counterclockwise 7 divisions. Determine the measurement.

Show answer

−0.007 in (counterclockwise means smaller than the reference).

Exercise 3: Reading an Inch Dial Gauge (With Turns Counter)

Example (Solved)

Turns counter = 2 revolutions
Main dial = 35 divisions
Measurement = (2 × 0.100) + (35 × 0.001) = +0.235 in

(Corrected in this edition: the original printing ignored the two full revolutions and reported +0.035 in.)

Student Practice

Turns counter = 1 revolution
Main dial = 62 divisions
Determine the measurement.

Show answer

(1 × 0.100) + (62 × 0.001) = +0.162 in
(Corrected in this edition: previously printed as +0.062 in.)

Exercise 4: Metric Dial Gauge Reading

Example (Solved)

Turns counter = 3 revolutions
Main dial = 14 divisions
Measurement = (3 × 1 mm) + (14 × 0.01 mm) = +3.14 mm

(Corrected in this edition: the original printing ignored the three full revolutions and reported +0.14 mm.)

Student Practice

Turns counter = 2 revolutions
Main dial = 47 divisions
Determine the measurement.

Show answer

(2 × 1 mm) + (47 × 0.01 mm) = +2.47 mm
(Corrected in this edition: previously printed as +0.47 mm.)

Exercise 5: Inspection Decision

Example (Solved)

Specification = ±0.015 in
Dial gauge reading = −0.006 in
Conclusion: Part is in specification

Student Practice

Specification = ±0.08 mm
Dial gauge reading = +0.12 mm
Determine whether the part is in specification.

Show answer

Out of specification — +0.12 mm exceeds the +0.08 mm limit.

Chapter 5 Self-Check

Answer all three questions, then select "Check my answers."

1. Dial gauges are best described as what kind of instrument?
2. On a 0.001 in gauge (0.100 in per revolution), the turns counter shows 1 and the dial shows 40 divisions clockwise. What is the reading?
3. Where should a dial gauge be zeroed?

Chapter 5 Resources

Dial gauge and indicator demonstrations (external videos, optional enrichment):