Pressure is the force opplied per unit of area in a system. The total pressure in a system is equal to the barometric pressure plus the atmospheric pressure. Barometric pressure is the pressure that is being read by a device. So, in this case, the baramoteric pressure is equal to 61 mmHg.
The total pressure would be 61 mmHg + 779 mmHg = 840 mmHg.
