I have imported customers and customer-branches, that is OK now.
I have figured out that for importing products you need to fill 6 tables (or 7)
in a coherent way.

stock_master
item_codes
purch_data
prices
stock_moves
loc_stock

Now if I want 1000 pieces of a product in stock I must put that in stock_moves.

I am not sure that I have to put something in gl_trans

since there is no connection to the productnumber there, with wat is it connected then
and am I obliged to put a -1000 and +1000 line in there?

Kind regards,
Jan