A method for a CPR training, the method comprising: providing a manikin comprising an interior structure and a removable skin fitted over the interior structure, the interior structure comprising a frame corresponding to a rib cage of a human body; providing a compression pad comprising a housing, at least one force sensor, at least one acceleration sensor housed within the housing, the at least one force sensors configured to detect force applied thereto, the at least one acceleration sensor configured to detect acceleration applied thereto; lifting or removing the skin to expose at least part of the frame; subsequently placing a compression pad over the frame; subsequently fitting the skin over the interior structure such that the compression pad is located in the manikin's chest region under the skin; performing a sequence of initializing compressions onto the manikin's chest region, which applies force and acceleration that the at least one force sensor and the at least one acceleration sensor can detect respectively; providing initializing force signals generated by the at least one force sensor and initializing acceleration signals generated by the at least one acceleration sensor in response to the initializing compressions; processing the initializing acceleration signals to generate initializing displacement signals representing displacement of the compression pad caused by the initializing compressions; processing the initializing force signals and the initializing displacement signals to provide a correlation between displacement of the compression pad and force applied to the compression pad by the initializing compressions; subsequently, performing a CPR training session comprising a sequence of training compressions onto the manikin's chest region, which applies force and acceleration that the at least one force sensor and the at least one acceleration sensor can detect respectively; providing training force signals generated by the at least one force sensor in response to the training compressions; and computing displacement caused by the training compressions using the training force signals and the correlation between displacement and force by the initializing compressions, wherein computing displacement does not use acceleration signals generated by the at least one acceleration sensor in response to the training compressions. providing a manikin comprising an interior structure and a removable skin fitted over the interior structure, the interior structure comprising a frame corresponding to a rib cage of a human body; providing a compression pad comprising a housing, at least one force sensor, at least one acceleration sensor housed within the housing, the at least one force sensors configured to detect force applied thereto, the at least one acceleration sensor configured to detect acceleration applied thereto; lifting or removing the skin to expose at least part of the frame; subsequently placing a compression pad over the frame; subsequently fitting the skin over the interior structure such that the compression pad is located in the manikin's chest region under the skin; performing a sequence of initializing compressions onto the manikin's chest region, which applies force and acceleration that the at least one force sensor and the at least one acceleration sensor can detect respectively; providing initializing force signals generated by the at least one force sensor and initializing acceleration signals generated by the at least one acceleration sensor in response to the initializing compressions; processing the initializing acceleration signals to generate initializing displacement signals representing displacement of the compression pad caused by the initializing compressions; processing the initializing force signals and the initializing displacement signals to provide a correlation between displacement of the compression pad and force applied to the compression pad by the initializing compressions; subsequently, performing a CPR training session comprising a sequence of training compressions onto the manikin's chest region, which applies force and acceleration that the at least one force sensor and the at least one acceleration sensor can detect respectively; providing training force signals generated by the at least one force sensor in response to the training compressions; and computing displacement caused by the training compressions using the training force signals and the correlation between displacement and force by the initializing compressions, wherein computing displacement does not use acceleration signals generated by the at least one acceleration sensor in response to the training compressions.