An interesting note: "preciso" translates as BOTH accuracy AND precision, which are COMPLETELY different concepts in English.
In technical schools, we learn the difference between "precisão" (precision) and "exatidão" (accuracy), but in common life they are not very well distinguished.
To be fair, many English speakers (some more than others, cough-cough) have this problem, too.
It has both meanings (accurate/precise, and necessary/needed), both work in this context.
Although true, it's very unlikely to see such a sentence without complements meaning "necessary".
I used watch and it was accepted, but necessary was not, even though it is one of the translations....
You can report that too. "Necessary" or "needed" is another meaning of the word "preciso" and it makes sense in this context.
If the meaning of the sentence is "the clock is accurate" then commonly accepted ways of saying this in English would include the clock is right or correct. If the clock is precise then this suggests the ability to distinguish between small fractions of a second. Perhaps an atomic clock or similar. The suggestion that the clock could be "sharp" would mean that the edges could cut your fingers but in parts of England might give the idea that the clock was running fast.