Multispot Temp Element

That sounds weird. If there is any water in the tank, the bottom level of the water will be the same as the bottom of the tank. Duh.

Just to clarify is the Agar interface meter a brand ? Or are you talking about some nutrient gel that might be heavier than water.

As Tornado pointed out water is almost always heavier than crude oil and so will be the bottom layer and so the bottom of the water layer will be the bottom of the tank.

However if you are measuring the TOP of the water layer then yes this will be the same as the water / oil interface.

You need to be sure that the instruments can be cross referenced depending on how they measure height - differential pressure; transit time floating bobs etc

If yo have some gel / semi solid material this could be heavier than water and so be the bottom layer

In your case, the bottom of the water sensor range is the tank bottom, and the top of the water level is the interface level. Suggest you re-think the question, since it is highly likely you will answer your own query...