(568:64).683

Do you mean (568:64) × 0.683? If so, the colon is division:

• 568:64 = 568/64 = 71/8 = 8.875
• 0.683 = 683/1000

Thus (568:64).683 = (71/8) × (683/1000) = (71 × 683) / 8000 = 48493/8000 ≈ 6.061625.

If you meant something else (e.g., 568:64.683 as a single ratio), let me know and I’ll recalc.