Year-end level from BEA, Fixed Asset Table 4.1 Current-Cost Net Stock of Private Nonresidential Fixed Assets by Industry Group and Legal Form of Organization; line 50, Nonprofit institutions, Equipment and software. Other quarter's levels are derived from year-end level, plus the quarterly unadjusted flow calculated as gross investment (FOF series FU165013023) less depreciation (FOF series FU166330023), plus an estimate of capital gains based on NIPA, table 1.1.4 Price Indexes for Gross Domestic Product, line 11, Nonresidential, Equipment and software.