Student descriptions of the key bending event. Impossibility of describing everything. Observation has to be selective. Problem of relevance. Informal observation is retrospective, unsystematic, and contaminated by the limitations and quirks of human memory and cognition. Scientific observation is prospective, planned, systematic, calibrated and productive of trustworthy data.
A companion course guide can be downloaded here: http://jref.swmirror.com/20730