on nose

Two friends are talking ...

Friend 1: You said that you would arrive at six o'clock.

Friend 2: And what time is it now?

Friend 1: Six o'clock on the nose.

Friend 2: There you go. I am exactly on time.

A question: what does "on nose" here in this context?  谁能猜到 on nose 是什么意思？

a/  在鼻子上

b/ 正好地

c/ 还差一点 

d/ 晚了一点