tax procedure

hi guru's,

1.In determination of excise duty >basic settings, for tax procedure TAXINJ can I add condition for calculation of customs duty,if yes, which condition type i can copy.

2. Again on same screen for tax default informations,for calculation of additional tax there are three colums,

a)A/P AT1 cond.

b)A/R AT1 cond.

c)AT1 Perc.

Why we maintain these three columns.

regards,

vandana