Percentage Contrast and Percentage Background Variability of Spheres
| Diameter (mm) | Contrast (%) | Background variance (%) |
| 10 | 32.5 ± 5.1 | 5.3 ± 1.0 |
| 13 | 50.0 ± 9.2 | 4.8 ± 0.8 |
| 17 | 62.9 ± 7.2 | 4.2 ± 0.5 |
| 22 | 70.8 ± 6.0 | 3.7 ± 0.3 |
| 28 | 65.1 ± 1.2 | 3.3 ± 0.2 |
| 37 | 72.3 ± 1.1 | 3.0 ± 0.1 |