Freesurfers-

When choosing the simulation type does the ending have to match the sim sign? for instance i see examples with 

--sim mc-z 10000 3 mc-z.pos.3 --sim sign pos

or 

--sim mc-z 10000 3 mc-z.neg.3 --sim sign neg

I guess what i am asking is what does the first sign (in the mc-z.(SIGN).3 mean?

michael