Please add ?nation=(your nation name) to the url to get it to work properly (Remember, spaces should become "%20", HTML-encoded).
Other options:
&popspec=(the difference of your "population" from Nationstates) - For those countries who like to specify exact populations
&randomize=1 - Randomizes the GDP per capita and budget (and population if there's no popspec) slightly
&defenseprovided=1&defense=(percentage of your GDP spent on defense) - Calculates your Defense spending. REQUIRES DEFENSEPROVIDED TO BE SET.
&militarybudget=1 - Forces &defense= to represent the percentage of your budget instead of your GDP. MUST BE USED WITH THE TWO ABOVE VARIABLES.