As data can be compressed, we inquire if time can also be compressed. In the context of manufacturing systems, time compression adopts such names as "concurrency" or "simultaneity". While it may be intuitively appealing that scaling (halving the size of a task, for example) should be linear (halving the time), such is not quite the case, as we have discovered. We report a quantitative explanation for the nonlinear behavior of time, as a function of the size of a task and the number of agents performing the task.

The paper surveys the current state of knowledge of techniques for representing, manipulating and analysing dimensioning and tolerancing data in computer-aided design and manufacturing. The use of solid models and variational geometry, and its implications for the successful integration of CAD and CAM, are discussed. The topics explored so far can be grouped into four categories: (a) the representation of dimensioning and tolerancing (D & T), (b) the synthesis and analysis of D & T, (c) tolerance control, and (d) the implications of D & T in CAM. The paper describes in detail the recent work in each group, and concludes with speculation on a general framework for future research.