ISO 18213-4:2008规定了在配备有气动系统以测定液体含量的核材料计量箱中准确测定液体高度的程序。在这种系统中，气体被迫通过探头（浸入管），探头的尖端浸没在储罐液体中。诱导起泡所需的压力是用距离探针尖端一定距离的压力计测量的。当采用非常缓慢的起泡速度时，该程序特别适用。

ISO 18213-4:2008 specifies a procedure for making accurate determinations of the liquid height in nuclear-materials-accountancy tanks that are equipped with pneumatic systems for determining the liquid content. With such systems, gas is forced through a probe (dip tube) whose tip is submerged in the tank liquid. The pressure required to induce bubbling is measured with a manometer located at some distance from the tip of the probe. This procedure applies specifically when a very slow bubbling rate is employed.