Does the red line exactly in the middle of the Altar prove that one can be exact? - No, it doesn't, for perhaps it was intentionally drawn thicker to account for error.
If one breaks a ritually impure clay oven into pieces, the pieces are pure, but if he divides it exactly in half, both pieces remain impure - because one piece is the larger one and is impure, only we don't know which. Thus, precision is impossible!? - No! clay has jugged edges, but perhaps with other materials one can be precise.
If a murder victim is found exactly between two cities, they jointly bring a calf for atonement - because in reality the body is closer to one city - which makes this city obligated to bring the calf - only we don't know which one. This proves that one cannot be precise!? -- Yes, it does.
Art: Pancraz Koerle - The Broken Vase