Abstract: An apparatus for measuring parameters of work diagram of piston machines comprises, connected to one another, a current crankshaft rotation angle counter having inputs coupled, via a crankshaft angular position pulse former and a top dead center pulse former, to an angular mark sensor, and a decoder decoding top dead center signals. To the latter is coupled an input of a flip-flop of an analysis and control unit which also has a counter having an input coupled, via a main coincidence gate, to one of n pressure sensors in cylinders of piston machines, in accordance with the cylinder selected for indication, and a logical circuit having an input coupled to a reversible counter connected to a flip-flop. The apparatus also comprises a series circuit including a decoder for decoding bottom dead center signals coupled to the reversible counter and flip-flop, a cycle length counter and a main flip-flop coupled to the bottom dead center decoder and to an AND gate.