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Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Fill level estimated vs. fill level reported in earlier studies. Orange dotted line (......) represents the x = y line, green dots (◆) represent the estimated fill level values, and black dotted lines (- -) represent the 5% error margins.