Thanks for your input. While searching for products I've come across dozens of patents, but it appears very few have found their way into the market. It is a bit surprising that such a relatively simple process control solution should be so expensive to implement.
I think I have a general idea how to use a dipstick, too. All I am trying to do is make dipping the tank even simpler for me.
As for the 'keep it simple' train of thought, Einstein said: "Things should be made as simple as possible, but not simpler."