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How to Use a Dial Test Indicator
Guide · Updated October 28, 2026
A dial test indicator (DTI) has a lever stylus that swings in an arc, so it reaches into bores and along faces where a plunger indicator can't. It is the go-to tool for tramming, truing vises and indicating parts.
Trust the readings
Check your test indicator against gage blocks; the free Gage Block Calculator builds the step stacks.
Step by step
- Mount it rigid: Hold it in a short, rigid arm or a spindle holder.
- Set the stylus: Set the stylus nearly parallel to the surface, within about 10–15°.
- Preload: Touch the surface and preload about a quarter turn.
- Zero: Rotate the bezel to zero.
- Sweep: Move the work or indicator slowly along or around the surface.
- Read the change: Read total indicator reading (TIR), not the absolute number.
- Adjust and repeat: Adjust the part and recheck until within tolerance.
Worked example
Stylus at 30° to the surface reads 0.0010 in. The cosine correction is cos 30° ≈ 0.866, so the true change is about 0.00087 in. At 10°, the error is under 2%.
Test indicator vs plunger indicator
A DTI is for comparisons over small ranges in tight spots. A plunger dial indicator has more travel and reads direct for height or depth.
Direction lever
Many DTIs have a lever or work both directions automatically. Make sure the stylus is reading in the direction you push.
Tips
- Learn cosine error.
- Check accuracy with gage blocks.
- Use it to indicate a vise or tram a mill.
- Don't bump the stylus past its range.
FAQ
What is a dial test indicator used for?
Comparing surfaces — tramming, truing vises, indicating bores and checking runout.
What angle should the stylus be?
As close to parallel to the surface as practical, within about 10–15°.
Is a test indicator the same as a dial indicator?
No, a test indicator uses a lever stylus; a dial indicator uses a plunger.
What is cosine error?
Reading error from the stylus angle; multiply the reading by the cosine of the angle.
How much preload should I use?
About a quarter turn of the dial.
Related guides and calculators
- How to Use a Dial Indicator
- Cosine Error with Indicators
- How to Check a Test Indicator with Gage Blocks
- How to Tram a Mill
- How to Indicate a Vise True
- How to Indicate a Bore True
- Magnetic Base Indicator Setup
- Runout and TIR Basics
- How to Set Up a Milling Vise
- How to Cut a Taper on a Lathe
- How to Indicate a Fixture
- How to Use a Cathead on a Lathe
- How to True a 3-Jaw Chuck
- All free machinist calculators
- Precision Level Basics
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