The U.S. economy contracted 5% in the first quarter of 2020. With the coronavirus crisis continuing into the summer, economists are expecting an even steeper contraction in the second quarter. WSJ’s Carter McCall explains how GDP is calculated and how the coronavirus is impacting the equation. Photo Illustration: Jacob Reynolds/WSJ The U.S. economy could take the better part of a decade to fully recover from the coronavirus pandemic and related shutdowns, a U.S. budget agency said, as a series of surveys pointed to continuing weakness in global manufacturing. The Congressional Budget Office, a nonpartisan legislative agency, said the sharp contraction triggered by the coronavirus caused it to mark down its 2020-30 forecast for U.S. economic output by a cumulative $7.9 trillion, or 3% of gross domestic product, relative to its January projections. GDP…