A 1-bit flag that stores the results of the arithmetic logic unit (ALU) or parallel logic unit (PLU) test bit operations. The TC bit is affected by the APL, BIT, BITT, CMPR, CPL, LST #1, NORM, OPL, and XPL instructions. The status of the TC bit influences the execution of the conditional branch, call, and return instructions. This bit is stored in status register 1 (ST1).