No, not the compass you'd want if you were lost in the woods. This is more like the compass for finding your way out of a geometry book. A mathematical compass (like this one) is used to draw perfect circles. For Donne, it was the perfect metaphor for the long-distance relationship he imagined with his wife.
Line 26: The compass is introduced emphasizing two crucial features. First, compasses are firm or "stiff." They do their job and don't flinch. Second, they are two separate pieces that are permanently joined together to accomplish great things. Who knew math was so romantic?
Line 27-32: Donne claims that his wife is like the center, "fix'd" foot of the compass that stays rooted while the other runs away. It remains right there, providing stability and certainty to the circle. Not only that, "it leans" after the other foot.
Line 33-36: He shifts back to himself and applies the symbol of the other foot to himself. That's the part of the compass that leaves and traces the circle. At every point, he emphasizes that his wife (the center foot) is what is responsible for everything turning out right (good call, John). Because of that center foot, he makes a "just" or perfect circle and ends us safely back at home.