← AskMachinist · Guides · Calculator · 🔎 Search
Precision Level Basics
Guide · Updated October 28, 2026
A precision (machinist) level reads small slopes using a sensitive vial, often 0.0005 in per foot per division. It's used to level lathe beds, machine tables and setups.
Check the base
Verify flat surfaces with gage blocks; the free Gage Block Calculator builds the stacks.
Step by step
- Know the sensitivity: Read the vial rating, for example 0.0005 in per foot per division.
- Clean the surfaces: Wipe the level base and the surface.
- Let it settle: Let the bubble settle and avoid warming it with your hands.
- Read the bubble: Count divisions the bubble is off center.
- Reverse it: Turn the level 180° in the same spot and read again.
- Average: The average of the two readings is the true slope; the difference shows the level's own error.
- Adjust: Adjust the machine feet or screws and recheck.
Worked example
0.0005 in/ft level reads 2 divisions high to the right on a 3 ft bed: slope is 2 × 0.0005 = 0.001 in per foot, so 0.003 in over the 3 ft length.
Leveling a lathe
Level across the bed at the headstock and tailstock ends. Matching readings remove twist, which is what causes taper — true level matters less than no twist.
Level vs flat
A level shows slope relative to gravity; it does not show flatness. Use a surface plate and indicator for flatness.
Tips
- Always reverse the level to cancel its error.
- Recheck after tightening hold-downs.
- Align the tailstock afterward: tailstock alignment.
- Store it in its case away from heat.
Worked example: leveling a lathe bed for twist
Place a 0.0005 in/ft level across the ways at the headstock and read 1 division high at the front, then at the tailstock read 1 division low at the front. The change is 2 divisions, or 2 × 0.0005 = 0.001 in per foot across the bed: that is twist. Adjust the leveling screws at the tailstock end until both readings match, then turn a test bar and check the diameter at both ends with a micrometer to confirm.
FAQ
What does 0.0005 in per foot mean?
Each division of bubble movement means a slope of 0.0005 in over 12 in.
How do I check if my level is accurate?
Reverse it 180° in the same spot; readings should match.
Does a lathe need to be perfectly level?
It mainly needs no twist between ends; level makes that easier to check.
Is a carpenter level good enough?
No, it is far too coarse for machine setup.
Can a level check flatness?
No, it checks slope; use a surface plate and indicator for flatness.
Related guides and calculators
- How to Align a Lathe Tailstock
- How to Tram a Mill
- How to Use a Surface Plate
- Flatness and Parallelism Checks with Gage Blocks
- Surface Plate Care and Checking
- How to Check Squareness
- How to Use a Dial Test Indicator
- Gage Block Temperature Compensation
- How to Balance a Grinding Wheel
- Hand Scraping Basics
- How to Level a Lathe Bed
- All free machinist calculators
Build your stack in seconds
The free Gage Block Calculator finds the fewest-block combination for inch and metric sets, with wear blocks. No login.
Questions? Ask a machinist.
General shop information only — follow your machine and tooling manufacturer's instructions and your shop's safety rules.