3/ Surface form tolerance
Code 3/ limits how far a surface may deviate from its nominal shape. It is written in the field of the surface it applies to.
Standard: ISO 10110-5
Syntax
| 3/A(B/C) | A = max. power deviation (PV; “sagitta error” in older editions), B = max. irregularity (PV), C = max. rotationally invariant irregularity (PV). |
| 3/A(B) | Without C. |
| 3/—(B) | A dash for A: the power tolerance is carried by the radius tolerance. |
| 3/A(B/C) RMSx < D | Adds an rms limit; x = t (total), i (irregularity) or a (rotationally varying). |
| ; λ = E | Required when the values are in fringe spacings; nanometres are the preferred unit since the 2015 edition. |
Worked examples
| 3/ 2(0.5); λ = 632.8 nm | 2 fringes power, 0.5 fringe irregularity at 632.8 nm. |
| 3/ 600 nm (300 nm/150 nm) | 600 nm power, 300 nm irregularity, 150 nm rotationally invariant irregularity. |
| 3/ —(0.5) RMSi < 0.1; λ = 632.8 nm | Power via the radius tolerance; 0.5 fringe irregularity PV and rms irregularity < 0.1 fringe. |
| 3/ 5(1); λ = 632.8 nm | 5 fringes power, 1 fringe irregularity. |
Click an example to open it in the decoder.
Common values and typical grades
| Commercial | 3/ 5(1) to 3/ 3(1) fringes at 632.8 nm |
| Precision | 3/ 2(0.5) |
| High precision | 3/ 1(0.25) or tighter, often with an RMS limit |
Typical shop practice, not values from the standard; capabilities vary by size and material verify. One fringe spacing = λ/2 of surface height (316.4 nm at 632.8 nm). ISO 10110-5:2026 (4th edition, published 2026-05) adds a “waves” unit, slope and Zernike residual indications; the forms above are the 2015 basic forms verify.
Common mistakes
- Giving fringes without a wavelength. Older editions assumed 546.07 nm; write
; λ = 632.8 nmor use nm. - Tolerancing the radius and giving a power value A for the same thing. Use a dash for A if the radius tolerance controls power.
- Specifying irregularity larger than power, or an irregularity your shop cannot measure on that aperture.
- Writing
λ/4instead of the 3/ notation.
Questions
What does 3/ 2(0.5) mean?
Surface form tolerance: at most 2 fringe spacings of power deviation and 0.5 fringe spacing of irregularity, peak-to-valley. With fringes, the test wavelength must be stated, e.g. “; λ = 632.8 nm”.
What does the dash in 3/ —(0.5) mean?
No power tolerance is given in fringes; power is controlled by the radius tolerance written with the radius.
Which edition of ISO 10110-5 is current?
ISO 10110-5:2026, the 4th edition, published May 2026 per the ISO catalogue. It replaced the 2015 edition.
Sources
ISO 10110-5:2015 (public preview); ISO 10110-5:2026 (4th ed.) catalogue entry and preview. Full list and edition status: Sources & editions.
An unofficial summary written from public previews of the standards and reputable secondary sources. It does not reproduce the ISO text. Items marked verify could not be fully confirmed. Check against the current edition; see Sources & editions.