[Limdep Nlogit List] how I know the coefficient of third level?

[spchiou]

Dear all:
     I have a qualitative variable "grad" in my model. This variable have 3 
level, and I use grad1 and grad2 to code it. Now, I have problem about third 
level, I can explain grad1 and grad2 by their coefficient, but how about the 
third level? I codding level with (1,0),(0,1),(-1,-1) in the data.
     Is the third level is base level, so we can't get it's coefficient? and 
what the different when I codding level with (1,0),(0,1),(-1,-1) and (1,0),
(0,1),(0,0)?
Please help me?