Calculator
ANSI tolerance checker
Enter the ordered prescription and the measured values from the lensometer for both eyes; each parameter is checked against the ANSI Z80.1 tolerances as commonly published. The axis allowance tightens with cylinder power: 14 degrees at 0.25 D or less, 7 to 0.50 D, 5 to 0.75 D, 3 to 1.50 D, and 2 degrees above 1.50 D. Verify the edition in force before applying figures to real work.
ANSI tolerance checker
Enter the ordered and the measured values for each eye. Each parameter is checked against the ANSI Z80.1 tolerances as commonly published; axis deviation wraps the 180 degree scale, so 178 against 002 reads as 4 degrees.
OD (right eye)
OD: PASS
| Parameter | Ordered | Measured | Deviation | Tolerance | Result |
|---|---|---|---|---|---|
| sphere | -2.00 | -2.12 | 0.12 D | +/- 0.13 D | pass |
| cylinder | -1.50 | -1.50 | 0.00 D | +/- 0.13 D | pass |
| axis | 180 | 177 | 3 deg | +/- 3 deg | pass |
OS (left eye)
OS: PASS
| Parameter | Ordered | Measured | Deviation | Tolerance | Result |
|---|---|---|---|---|---|
| sphere | 0.00 | 0.00 | 0.00 D | +/- 0.13 D | pass |
| cylinder | 0.00 | 0.00 | 0.00 D | +/- 0.13 D | pass |
Training aid only. Verify the edition of ANSI Z80.1 in force at your laboratory before applying tolerances to real work.
Go deeper
The full bracket table with the boundary conventions is in the ANSI tolerance reference. Reading the measured values off the instrument is covered in reading a lensometer.
Frequently asked questions
What tolerances does the checker use?
Values per ANSI Z80.1 as commonly published for finished single-vision lenses: sphere plus or minus 0.13 D through 6.50 D (2 percent above), cylinder power plus or minus 0.13 D through 2.00 D, 0.15 D to 4.50 D and 4 percent above, and a cylinder axis table that tightens from 14 degrees at 0.25 D or less down to 2 degrees above 1.50 D. Verify the edition in force before applying tolerances to real work.
How is the axis tolerance decided?
By the cylinder power: the stronger the cylinder, the more a small axis error blurs, so the allowance tightens. Over 1.50 D of cylinder only 2 degrees is allowed; at 0.25 D or less the allowance is 14 degrees.
Does an axis of 179 versus an order of 2 fail automatically?
No. Axis wraps around the 180 degree scale, so 179 and 2 are only 3 degrees apart. The checker measures the shortest angular distance.
Is this checker a substitute for the published standard?
No. It is a training aid using commonly published values. Laboratories verify against the current edition of the standard and any stricter job requirements.