Any errors in sentences

It probably can be argued that "Hence, the wearer need not wind it." is a sentence fragment.

Thanks, Frank.

I wanted to change to 'watch', but I forgot until I saw your reply.

Am I correct to conclude that other than the above ambiguity, the sentence is fine?

Many thanks.

It's not an ambiguity. "it" is fine in the last sentence, which is, in fact, a sentence, I think. I think what Frank is talking about is the "Hence" part. I don't think you need to have that be part of another sentence, as in "the motion of the wearer's arm keeps it going, hence the wearer doesn't need to wind it." I think it's fine by itself as a separate sentence. You could also start it with "ergo" or "Therefore", or "So" ("so" actually probably be the most commonly used of those words--if you did use "so" you'd probably make it part of the previous sentence).

The sentence is fine. I'm sure we can quibble with the style, but there are no actual errors.

I think you should just make it into a single sentence. The fragment is not really a sentence...just a clause. Take out the period...substitute a comma, semi colon, or em dash--and change the capital H to a small "h."

Respectfully disagree with Frank.

No need to be respectful, McTag. Just tell us why you disagree.

"The wearer need not wind it" is a sentence. Adding "hence" makes no difference to that, imo.

I wouldn't bet the farm on it...but I think you are wrong.

Respectfully, of course.