Abstract: Determination is made of the amount of liquid housed within a vessel subject to intermittent dynamic forces wherein the liquid in the vessel may be being discharged intermittently. The fluid in the vessel has a liquid level above which is a vessel headspace. A sensing tube of substantially less volume than the vessel is provided. This tube also is subject to the intermittent dynamic forces. The tube has tube headspace that is held at the same pressure as the vessel headspace, e.g., atmospheric pressure. The sensing tube is fitted with a sensor assembly for measuring the level of liquid therein. The tube is in fluid communication with the vessel through an orifice in the vessel whereby the fluid level in the vessel is the same as the fluid level in the tube. The size of the orifice is such that the tube fluid level measured by the sensor assembly is substantially unaffected by the intermittent dynamic forces.