Metaphor in A Valediction: Forbidding Mourning

A Valediction: Forbidding Mourning 1
"wilt thou be to me,..."   (A Valediction: Forbidding Mourning)

In this metaphor, the speaker compares his lover to the fixed foot of the compass and himself to the free foot of the compass, suggesting that though he is away physically, he is still tethered to her. Like the compass, she will be his guide leaning after him and keeping him on track as he roams.