Retopology while using B surfaces and mirroring to the other side.

How do I mirror whatever I retopologize using B surfaces to the other side. I’ve seen it in the video demonstration but I don’t see how it’s done. The video is sort of blurry. Step by step please, if it’s currently possible to mirror. Thank you.

I usually just build half the mesh and then mirror it the old way: shift D ( duplicate ) m ( mirror ) x ( along x axis ) reposition, remove doubles, and recalculate normals

Start retopology. On the mesh you have created - select vertice closest to whatever will be your symmetry axis, go object mode and click Origin - Origin to 3d cursor on T-panel. Add mirror modifier while in object mode. Switch edit mode, adjust symmetry line vertices and continue to retopo.

Thank you so much, It worked like a charm : ) Sir, you have a nice day.

Make sure your object is at 0 on the axis you’re mirroring on