Say you roll on table one... and it has options 1-6. And for each result, there is another table... say 1A-1D, 2A-2D,...,6A-6D. so there are now 24 options. For sanity... we will say that 1s are twice as likely to come up, and As are twice as likely to come up. so... you make one big rollable table. You weight 1A by 4, 1B by 2, ... , 1D by 2, 2A by 2, 2B by 1, ... , 3A by 2, 3B by 1, ... , 6A by 2, 6B by 1, ... , 6D by 1. then when you roll off the table the various chances of each thing come out right. It gets messier the more involved the table becomes, and API only if you include the old "100 = roll twice on this table ignoring further 100s" line.