Optical Flatness Comparison Chart
| Fringe | Waves | Microns | Angstroms | Microinches | Inches | Parallelism Seconds |
| 1/10 | 1/20 | .025 | 250 | 1 | .000001 | 0.2 |
| 1/5 | 1/10 | .050 | 500 | 2 | .000002 | 0.4 |
| 2/5 | 1/5 | .100 | 1,000 | 4 | .000004 | 0.8 |
| 1/2 | 1/4 | .125 | 1,250 | 5 | .000005 | 1.0 |
| 1 | 1/2 | .250 | 2,500 | 10 | .000010 | 2.0 |
| 2 | 1 | .500 | 5,000 | 20 | .000020 | 4.0 |
| 3 | 1 1/2 | .750 | 7,500 | 30 | .000030 | 6.0 |
| 4 | 2 | 1.000 | 10,000 | 40 | .000040 | 8.0 |
| 8 | 4 | 2.000 | 20,000 | 80 | .000080 | 16.0 |
| 10 | 5 | 2.500 | 25,000 | 100 | .000100 | 20.0 |
| 100 | 50 | 25.000 | 250,000 | 1,000 | .001000 | 200.0 |