How to align vertices 100% accurately? So there's a problem I'm facing every time I work with mirror modifier. When I'm shaping only half of the mesh I have troubles aligning vertices that must have '0' local coordinates.

The issue is when I'm selecting more than 1 vertex and set it coordinates to 0 here.


I get random values for each single vertex. Like this.



And so I have to set each vertex to '0' manually.
This is likely because the vertices are not aligned. The transform panel shows the median location of all selected vertices; setting it to 0 will move the whole selection as a unit: 



To align the vertices, scale them (S) to 0 along the axis you which them to be aligned along. So for the X axis, S X 0: