Search Params

If no search params are specified on the command line, the search depth for computer 1 is taken from parameters.txt.
 
s<depth> "selective" search to <depth> in midgame; higher in endgame.

This is the most common setting for Ntest (and the setting used by NBoard)

f<depth> "fixed depth" (sort of)
t<depth> "turbo endgame" - same as s in midgame but with deeper searches in the endgame
a<seconds> 
[;<WLD depth>]
spend <seconds> each search on 'a'verage.Optionally force WLD solve at a given depth
m<minutes> take a maximum of <minutes> per game ('m'atch time)

Each <search params> gets its own book. You can rename the books (e.g. rename the book, play a game at match time, then rename the book back). If you rename a fixed-ply book and make it deeper, the program will reevaluate all book positions at the deeper depth next time it starts up. So I never do this, except from/to match time.