1. A method for a CPR training, the method comprising: providing a manikin comprising a frame and a removable skin fitted over the 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 sensor configured to detect force applied thereto, the at least one acceleration sensor configured to detect acceleration applied thereto; lifting or removing at least a portion of the removable skin to expose at least part of the frame; subsequently placing the compression pad over the frame; subsequently fitting the removable skin over the frame such that the compression pad is located in a chest region of the manikin and interposed between the frame and the removable skin; performing initializing compressions onto the chest region, wherein each initializing compression applies an initializing force and an initializing acceleration to the compression pad, wherein the at least one force sensor detects initializing forces applied during the initializing compressions and generates initializing force signals in response to the initializing compressions, wherein the at least one acceleration sensor detects initializing accelerations applied during the initializing compressions and generates initializing acceleration signals in response to the initializing compressions; processing the initializing acceleration signals to generate initializing displacement signals representing initializing displacements of the compression pad during the initializing compressions; processing the initializing force signals and the initializing displacement signals to provide a displacement-force correlation between the initializing displacements and the initializing forces; subsequently, performing a CPR training session that comprises training compressions onto the chest region, wherein the at least one force sensor detects a training force applied to the compression pad in response to each training compression and generates a training force signal corresponding to the training force; and computing a training displacement using the training force signal and the displacement-force correlation between the initializing displacements and the initializing forces, wherein the training displacement is not computed based on a training acceleration applied to the compression pad during the training compressions.