Why is per capita income calculated …

The per capita income of all the countries are calculated in dollars because..
1.Dollar is an standard international currency.
2. It is the largest used currency in the world.
3. Dollar is the base currency for all export and import pricing.
4.The common currency system taking dollar as the base was devised to bring an homogeneity for studying the GDP of all countries with the same base.
5. Purchase power parity issues.
6. In todays market the currencies have a floating rate against dollar and the exchange rate varies with time. This may arise a confusion for studying the past figures whose exchange rate we may not know with respect to dollar. For example:
If in 2001, 1$=46.5₹
and
In 2018, 1$=62₹;
then
There would be a lot of confusion studying the data's of the year 2001 by international standards today if it had been represented in the local currency (INR in case of India)