InGa is an eutectic mixture of 75.5 % Gallium and 24.5 % Indium.
It is liquid at room temperature and an ideal replacement for the mercury in the strain gauges. It is far less toxic than mercury (in some countries the use of mercury is forbidden). Since the specific electrical resistance of GaIn is a few times lower than the resistance of mercury, the electronic measuring circuit of the plethysmograph has to be designed especially to achieve sufficient accuracy. The S.I VeinTest II has been developed for the use of GaIn straingauges. GaIn straingauges will normally not work with plethysmographs designed for mercury straingauges.