[sfepy] Material units in Modal Simulation

Hello,

I have a problem when running a modal simulation. There is not error, but the number of eingenvalues found is zero. May be the problem is realed to the units. The mesh is in mm, and young modulus is MPa (N,mm), poisson is adimensional. My question is the next, which units shoud have rho, Tons/mm3 or Kg/mm^3?

Thanks, Jesus Sanz