A set of formulas for interpreting the diamagnetic measurements of compact plasmoid in a conducting chamber is derived. The formulas are written in the form of an integral transformation relating the magnetic flux to the radial pressure profile of the plasmoid. An inverse transformation is also found. Particular examples of applying the newly derived formulas to the SHIP experiment are given. They show that the conductive chamber has essential effect on the result of the measurements. The optimization of the loop geometry that allows maximizing the measured signal is also described.