Method for dispensing and/or aspirating a predetermined volume of fluid, comprising: - providing a chamber comprising a lower portion and an upper portion, the lower portion for containing fluid, the upper portion being for containing gas, - providing an apparatus for dispensing and/or aspirating a predetermined volume of fluid from said chamber and being connected thereto such that an upper portion of the chamber is in fluid communication with a pump of the apparatus and such that the lower portion of the chamber is in fluid communication with a controllable valve of the apparatus; - providing fluid in the lower portion of the chamber and a volume of gas in the upper portion of the chamber; - measuring an initial pressure P 0 in the upper portion of the chamber by means of a pressure sensor of the apparatus; - introducing or evacuating a known quantity of gas into or out of the upper portion of the chamber respectively; - measuring a first pressure P 1 in the upper portion of the chamber by means of the pressure sensor; - determining the volume V 1 of gas in the upper portion of the chamber by means of said known quantity of gas, said initial pressure P 0 and said first pressure P 1; - determining a target pressure P 2 of the upper portion of the chamber, said target pressure being calculated so as to dispense or to aspirate a predetermined volume ΔV of fluid; - opening said controllable valve to dispense or aspirate a desired quantity of fluid while monitoring the pressure in the upper portion of the chamber by means of the pressure sensor; - closing said controllable valve once said target pressure P 2 is reached. - providing a chamber comprising a lower portion and an upper portion, the lower portion for containing fluid, the upper portion being for containing gas, - providing an apparatus for dispensing and/or aspirating a predetermined volume of fluid from said chamber and being connected thereto such that an upper portion of the chamber is in fluid communication with a pump of the apparatus and such that the lower portion of the chamber is in fluid communication with a controllable valve of the apparatus; - providing fluid in the lower portion of the chamber and a volume of gas in the upper portion of the chamber; - measuring an initial pressure P 0 in the upper portion of the chamber by means of a pressure sensor of the apparatus; - introducing or evacuating a known quantity of gas into or out of the upper portion of the chamber respectively; - measuring a first pressure P 1 in the upper portion of the chamber by means of the pressure sensor; - determining the volume V 1 of gas in the upper portion of the chamber by means of said known quantity of gas, said initial pressure P 0 and said first pressure P 1; - determining a target pressure P 2 of the upper portion of the chamber, said target pressure being calculated so as to dispense or to aspirate a predetermined volume ΔV of fluid; - opening said controllable valve to dispense or aspirate a desired quantity of fluid while monitoring the pressure in the upper portion of the chamber by means of the pressure sensor; - closing said controllable valve once said target pressure P 2 is reached.