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How to Check a Test Indicator with Gage Blocks
Guide · Updated October 27, 2026
A dial test indicator reads tiny differences over a short range. That makes it easy to check with gage blocks, as long as you control the stylus angle. Here's how to check one and how to deal with cosine error.
Build the test steps
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Test steps (81-piece inch set, 0.030 in indicator)
| Expected reading | Block |
|---|---|
| 0 (zero) | 0.100 |
| 0.0005 | 0.1005 |
| 0.001 | 0.101 |
| 0.005 | 0.105 |
| 0.010 | 0.110 |
| 0.020 | 0.120 |
Metric (88-piece set): zero on 1.000 mm, then use 1.005, 1.01, 1.05, 1.10, 1.20 mm.
Cosine error
| Stylus angle | Multiply reading by |
|---|---|
| 10° | 0.985 |
| 20° | 0.940 |
| 30° | 0.866 |
| 45° | 0.707 |
Keep the stylus near parallel to the surface, or correct each reading. This is the most common test indicator error in the shop.
Step by step
- Mount rigidly: Mount the indicator on a rigid stand or height gage over a clean surface plate.
- Set the stylus angle: Set the stylus as close to parallel with the block face as you can, ideally within about 10°.
- Zero on a base block: Zero on a base block such as 0.100 in or 1 mm.
- Step through small stacks: Slide in blocks that differ by known small amounts and record each reading.
- Correct and compare: Apply the cosine factor if the angle can't be avoided, then compare with the indicator's spec.
Checking a plunger indicator instead? See how to check a dial indicator. A flat, clean plate matters too: surface plate care and checking.
FAQ
How is a test indicator different from a dial indicator?
A dial test indicator has a lever stylus and a short range, often 0.030 in or 0.8 mm, and is used for sweeping and comparing. A dial indicator has a plunger and a longer travel.
What is cosine error on a test indicator?
When the stylus isn't parallel to the surface, the indicator reads high. True movement = reading × cos(angle). At 20° the true value is about 94% of the reading, and at 30° about 87%.
What steps should I use to check a 0.030 inch test indicator?
Zero on a 0.1000-size base, then use stacks that step up by small amounts, for example 0.1005, 0.101, 0.105 and 0.110 against 0.100, all from an 81-piece set.
Can I check a test indicator on a height gage?
Yes. Mount it on a height gage or rigid stand over a surface plate, then slide stacks of known small differences under the stylus.
Is there a free calculator for the stacks?
Yes. The Gage Block Calculator at gageblockcalc.com builds any stack from inch or metric sets, free with no login.
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Build your stack in seconds
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Questions? Ask a machinist.
General shop information only — follow your gage manufacturer's instructions and your quality system.