Precision levelPrecision level (spirit level)

≡Standards, measuring range and accuracy

Standard

JIS B 7510:1993 Precision levels^[1][2]

Measuring range

—Not confirmed in public sources

Resolution / graduation

• Sensitivity 0.02 / 0.05 / 0.1 mm/m (grade A square type)
• Definition The inclination needed to move the bubble one division. Expressed as height per 1 m of base. 1 arcsecond = 4.85 µm per m (≈ 5 µm). 0.02 mm/m ≈ 4 arcseconds, 0.05 mm/m ≈ 10 arcseconds, 0.1 mm/m ≈ 20 arcseconds

^[2][3]1 source, for reference

Accuracy (instrument error / maximum permissible error)

—Not confirmed in public sourcesJIS tables not checked

▦Types

◎Part names and functions

◷How to read the scale

1. Read the divisions at both ends of the bubble and take the average^[2][4]
2. Get the height difference from the sensitivityExample: nominal 200 (length 200 mm), sensitivity 0.02 mm/m → 1 division = 4 µm/200 mm^[4]

✋Usage steps

1. Checking the zero point (reversal method): place it on a reference surface plate and read the bubble, then reverse it 180° at the same spot and read again^[2]
2. If it reads the same position after reversal and is within the reference lines → no adjustment needed. Same position but outside the reference lines → the plate is tilted. Moves the same number of divisions left and right → correct the level's zero with the adjusting screw. Scattered → from the side with the larger error, correct half the maximum error on the level, then adjust the plate^[2]
3. When moving it on a workpiece, slide it rather than lifting it. Read only after the bubble has completely settled^[2][4]
4. How to measure straightness: place the level at the measuring position and read, slide it a little at a time and read through to the end, convert each reading to height and accumulate, and take the max minus min of the deviations from the straight line joining both ends as the straightness (11.2 µm in Obishi Keiki's example)^[4]

!Common measurement mistakes and countermeasures

✓Care, storage, inspection and calibration

Care and storage

• After use, rust-proof and put it in the storage box. Check sensitivity after a drop, etc.^[2]

Inspection and calibration

• Check accuracy periodically. Adjust the bubble size by tapping lightly with the secondary vial up (larger) or down (smaller)^[2]

The four patterns of the reversal method suit a diagram.

⇄Related instruments