adverb
one more; another one
Literal adverbial use meaning 'one more' or 'another'. In modern everyday speech, もう一つ is usually more natural; 今ひとつ here has a somewhat written or deliberate feel.
今ひとつ確認したい点があります。
There is one more point I would like to confirm.
今一つ例を挙げれば、この違い
If we give one more example, this difference is easier to understand.
adverb
not quite; not entirely; somewhat lacking
Common evaluative use for something that is almost acceptable but falls short. Often appears with negatives or mildly critical expressions such as 今ひとつ分からない, 今ひとつ足りない, or 今ひとつだ.
説明を聞いても、今ひとつ分からない。
Even after hearing the explanation, I still do not quite understand.
この料理は悪くないが、味が今ひとつだ。
This dish is not bad, but the flavor is not quite there.