“…We highlight that unique recovery of the first order perturbation appearing in higher order elliptic operators differs from analogous problems for second order operators, such as the magnetic Schrödinger operator. In the latter case, due to the gauge invariance of boundary measurements, one can only hope to uniquely recover dA, which is the exterior derivative of the first order perturbation A, see for instance [25,29,34,39] and the references therein among the extensive literature in this direction. Here, if we view A as a 1-form, then dA is a 2-form given by the formula…”