A method for determining at least one operating parameter of a device for extracorporeal blood treatment, wherein the parameter depends on the absolute pressure, comprising the steps: adjusting the ambient pressure in a closed container filled at least partially with an initial air volume or in a closed container filled at least partially with an initial air volume and at least partially with liquid, characterized in that the method additionally comprises the following steps: pumping a liquid into the closed container, which is filled at least partially with an initial air volume, by means of a sequence of at least two delivery strokes of a pumping means (8, 10, 12) with predefined displaced volumes, or pumping a liquid out of the container, which is filled at least partially with an initial air volume and at least partially with liquid by means of a sequence of at least two delivery strokes of a pumping means with predefined displaced volumes, calculating the total volume pumped after each delivery stroke, measuring the relative pressure in the container after each delivery stroke, assigning the total volume pumped after each delivery stroke effected and the measured value of the relative pressure in the container after each delivery stroke effected to a value pair for the delivery stroke effected, determining the absolute ambient pressure and determining the initial air volume in the container using the value pairs for the sequence of delivery strokes effected, calculating at least one operating parameter of the device for extracorporeal blood treatment, wherein the operating parameter depends on the absolute ambient pressure. adjusting the ambient pressure in a closed container filled at least partially with an initial air volume or in a closed container filled at least partially with an initial air volume and at least partially with liquid, characterized in that the method additionally comprises the following steps: pumping a liquid into the closed container, which is filled at least partially with an initial air volume, by means of a sequence of at least two delivery strokes of a pumping means (8, 10, 12) with predefined displaced volumes, or pumping a liquid out of the container, which is filled at least partially with an initial air volume and at least partially with liquid by means of a sequence of at least two delivery strokes of a pumping means with predefined displaced volumes, calculating the total volume pumped after each delivery stroke, measuring the relative pressure in the container after each delivery stroke, assigning the total volume pumped after each delivery stroke effected and the measured value of the relative pressure in the container after each delivery stroke effected to a value pair for the delivery stroke effected, determining the absolute ambient pressure and determining the initial air volume in the container using the value pairs for the sequence of delivery strokes effected, calculating at least one operating parameter of the device for extracorporeal blood treatment, wherein the operating parameter depends on the absolute ambient pressure. pumping a liquid into the closed container, which is filled at least partially with an initial air volume, by means of a sequence of at least two delivery strokes of a pumping means (8, 10, 12) with predefined displaced volumes, or pumping a liquid out of the container, which is filled at least partially with an initial air volume and at least partially with liquid by means of a sequence of at least two delivery strokes of a pumping means with predefined displaced volumes, calculating the total volume pumped after each delivery stroke, measuring the relative pressure in the container after each delivery stroke, assigning the total volume pumped after each delivery stroke effected and the measured value of the relative pressure in the container after each delivery stroke effected to a value pair for the delivery stroke effected, determining the absolute ambient pressure and determining the initial air volume in the container using the value pairs for the sequence of delivery strokes effected, calculating at least one operating parameter of the device for extracorporeal blood treatment, wherein the operating parameter depends on the absolute ambient pressure.