What is the difference between FMESH and MESH in MCNP?

[19matthew89]

TL;DR Summary

Difference between MESH card and FMESH card

Hi everyone,

I am struggling to understand the difference between FMESH and MESH.
FMESH is used to create a mesh superimposed with the geometry but...what does MESH? Is it only involved in weight-window generation and not needed for mesh tallies?

Thanks in advance for the clarification.

 

[Alex A]

I had a read and I'm pretty confident you are right. FMESH is a tally mesh, and MESH is a variance reduction mesh.