The construction of a force continuum for police officers is intended to guide them in using the appropriate type and level of force in a given situation. Various designs for force continuums have been developed. Linear designs tend to emphasize a sequential and escalating application of force until the desired outcome is achieved. Linear designs have been criticized for suggesting that officers first use ineffective force application prior to the one that eventually is effective. Modified linear continuums attempt to mitigate these shortcomings with a "branching" design that allows for a less rigid series of escalating levels and types of force. Non-linear continuums attempt to match types and levels of force with the types of resistance and threats being used by the subject. Another design is the "perceptual continuum," which focuses on officer perceptions of a situation as a significant factor in the kind of force an officer uses. This continuum is particularly useful in officer training, since it focuses on how officers' actions are related to the timing and accuracy of their perception of a subject's intentions. The author advises that when force continuums are used for training purposes, they must be continually assessed to ensure that they accurately reflect an agency's policy and procedure regarding the use of force.