Perhaps the manufacturer knows how to calibrate the device for different types of cables, but does not tell anyone. Has some pros: Everything you need is there, except for measuring the length. Has cons: Lies when measuring length. Hyperline cable UFTP4-C6-P26-IN-LSZH-GY-100 - 25 meters turn into 35. Cable ExeGate FUTP4-C6-CU-S23-IN-PVC-GY-305 FTP in a bay of 305 meters turned into 385.