Absrruct: Rigid body orientation can be estimated in a "sourceless manner" through the use of small three degree of freedom sensor modules containing orthogonally mounted triads of micromachined angular rate sensors, accelerometers, and magnetometers. With proper filter design, drift errors can be eliminated However, variations in the direction of the local magnetic field reference vector can cause errors in the estimated orientation. The experimental work described in this paper attempts to quantify these errors with an eye toward the development of corrective algorithms. To determine the types and magnitudes of errors that can be expected, three different types of inertiaVmagnetic sensor modules were subjected to controlled changes in the direction and magnitude of the local magnetic field. The amount of magnetic variation caused by several common objects was also measured in order to gain insight into the magnitude of errors that can be expected during operation in a typical environment. The experiments indicate that variations in the direction of the local magnetic field lead to errors only in azimuth estimation when using inertidmagnetic sensor modules. In a common roam environment, errors due to local variations caused by objects such as electrical heaters, CRT monitors, and metal furniture can be expected to be no more than 16 degrees. In most causes these errors can be avoided by maintaining a separation of approximately two feet from the source of interference.

The current study extends the mand-for-information literature by examining a method to teach mand-for-information frames, targeting 2 frames for the "How?" mand ("How do I?" and "How many?"). Using separate behavior chains to target the 2 frames, we taught 3 children with autism to emit mands for information with 1 behavior chain and assessed generalization with the remaining behavior chains. Behavior chains that the participants were unable to perform independently and that produced a desirable outcome for the participant (e.g., tornado water) were used to contrive the relevant motivating operation. For all 3 participants, mands for information generalized across motivating operations and response topographies.

Four children with autism received opportunities to choose among several preferred stimuli either immediately before or after task responding. The response requirement for reinforcement systematically increased within each session. Two children engaged in higher levels of responding when reinforcement choice was provided as an antecedent to task completion, and 3 of the 4 children showed a preference for the antecedent choice condition.

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The most recent attempt to explain Aristotle's use of in Poetics 13 is that of T. C. W. Stinton (CQ N.S. 25 (1975), 221–54). Stinton insists that must not be restricted to any one definition, but should be understood to include a ‘range of applications’ embracing both moral error and ‘ignorance of fact’ (p. 221).