Final answer:
Two key indicators used in the calculation of the HDI are life expectancy at birth and educational attainment, which respectively measure the potential for a long and healthy life and the level of education of a country's citizens.
Step-by-step explanation:
The Human Development Index (HDI) is a composite measure used to rank countries based on their human development levels.
In the calculation of the HDI, two of the key indicators used are life expectancy at birth, which serves as an indicator of the ability to live a long and healthy life, and educational attainment, which combines the adult literacy rate with the gross enrollment ratio for primary, secondary, and tertiary schools to assess the knowledge dimension of a country.
Life expectancy at birth reflects the overall mortality level of a population and provides an indication of the length of life that a newborn is expected to have if current mortality rates continue to apply.
Educational attainment is a measure of both the adult literacy rate and the combined primary, secondary, and tertiary gross enrollment ratio, representing the average education level of a country's population.
Other significant indicators, for reference, include Gross National Income (GNI) per capita at purchasing power parity (PPP), which denotes the standard of living or income dimension by capturing the average income of a country's citizens.