If the saline solution is mixed well enough, yes. If it's not because you didn't physically disturb it enough or you used cooler water, the salinity in one area is going to be different than another area. You would have to assume the person followed instructions to ensure it was properly mixed to a homogeneous state. In my opinion it would be simpler just to come up with an way of using an absolute amount of water and absolute amount of salt at an absolute temperature. That is to say, ensure the error in mixing is very small due to the simplicity and rigidity of the mixing process. I'm sure there's something like this out there, but I'm a computer engineer, not a chemist.