Taking a shot at specific gravity measurements

I get what you mean but I plan to make sure I always use the same volume by pumping more than the container can hold so the excess overspills. By example I mean, if you get a 1 litre container and pour 2 litres into it, there's still only going to be 1 litre in the container. By taking the measurement straight away and then flushing it should that not solve the issue of having to have exactly the same volume each time and by allowing a few seconds for it to settle and then taking the measurement straight away would that not prevent evaporation from having a noticeable influence? It might take some calibration to set up but I would think it was only required once.