The nominal value of the debt is not a good measure because it disregards the fact that the value of a single unit (the dollar) changes over time, and doesn't reflect the difficulty in paying it off (i.e. % of national GDP).
It's also a bit of apples-and-oranges when you compare the nominal debt of one country with another without looking at the differences in GDP between the countries, i.e. the size of each country's economy.
It's also a bit of apples-and-oranges when you compare the nominal debt of one country with another without looking at the differences in GDP between the countries, i.e. the size of each country's economy.