Jeff Stein from the Washington Post is out with an article saying that there were numerous formula to calculate the reciprocal tariff levels. The other ones were said to be more sophisticated. Although a can be confirmed precisely the one that train picked and similarities to ideas proposed by Peter Navarro.
Adam posted yesterday that the formula basically took the imports from the country and divided by the number of exports from the US. Then they halved that amount.
They did not take into consideration number of different factors like the US does not grow coffee beans or bananas (sans perhaps in Hawaii). Nor did it take into consideration the service surplus. That is just scatching the surface
Washington Post: Trump chose the formula for the tariffs