I want to fill the test-tube with the given liquids(A, B,C) based on the given readings.
During runtime the test-tube has to be filled using mouse press or using arrows on the keyboard with the coresponding liquids.

There may be some easier ways to do this, but if I had to do
this, I would create a model that "fits" into the test tube,
and animate the "top" vertices moving from a low postion
on the z-axiz(no liquid) to a higher position on the
z-axis (filled). Your interface could adjust the percentage
setting in ent_animate to correspond to the desired amount of liqud.

I would also set the alpha to 0 when there is not supposed to be
any liquid and increase it when it the fill level first increases.

Hope this helps.