  Computer mice have their displacement sensors in various locations (center,
front, and rear). However, there has been little research into the effects of
sensor position or on engineering approaches to exploit it. This paper first
discusses the mechanisms via which sensor position affects mouse movement and
reports the results from a study of a pointing task in which the sensor
position was systematically varied. Placing the sensor in the center turned out
to be the best compromise: improvements over front and rear were in the 11--14%
range for throughput and 20--23% for path deviation. However, users varied in
their personal optima. Accordingly, variable-sensor-position mice are then
presented, with a demonstration that high accuracy can be achieved with two
static optical sensors. A virtual sensor model is described that allows
software-side repositioning of the sensor. Individual-specific calibration
should yield an added 4% improvement in throughput over the default center
position.
