The drilling of a casing bit and any other equipment in the casing with another casing bit where at least two casing bits of different diameter and having associated casing sections may be assembled to form a drilling assembly for drilling subterranean formations, the at least two casing bits and casing sections are arranged in a telescoping relationship. Once a paper sheet present on the upstream side of a transport path relative to the loop-shaped part is fed to the loop-shaped part, the paper sheet present on the upstream side and the paper sheet present on the loop-shaped part are respectively moved, such that the paper sheet can be stacked with paper sheet circulated along the loop-shaped part. During a phase where one of the coils is in a high-impedance state, an induced voltage generated in the coil is detected.