This chapter is concerned with two problems. The first difference raises the problem of a comparison of levels of output. The second difference is concerned with comparative rates of growth. Countries differ both in the absolute size of their levels of output or income, and in the change in these levels over time. The reliability and comparability of the statistics varies considerably, and certain international institutions try to present them in standard, comparable forms. The trends in growth can be seen most clearly if the indexes are plotted on a ratio chart where similar vertical distances represent similar relative changes. Industrial production in industrial statistics means manufacturing and mining output. The output of a country is composed of a wide range of goods and services. The problem of comparisons between the levels of output in different countries is identical with the problem of comparing levels of output at different dates.