[Rivet] Rivet and HepMC units [Re: Rivet!!]

[David Grellscheid]

Hi Ben,

 > but I think realistically we are better off
 > sticking with the older HepMC for now

The newer one works just fine if it's told the right legacy units at 
compile time. The mistake is in configuring HepMC with MEV/MM when your 
legacy files are actually in GEV/MM.

I guess some other people in ATLAS actually do have HepMC files in 
MEV/MM lying around, again only implicitly assumed. This mess is only 
solved by the newer HepMC's 'U' line, which is why I would strongly 
recommend to move to it as soon as you can.

See you,

   David