Note: This web page is really old, and not being maintained any more, but I've left it up because it may be of use to some.
The most recent version of the GFLMB is version
1.1, which was released in March 1996.
This page last changed: January 29th, 1997.
Fitts' law models rapid, aimed, movements, where one appendage (like a hand) starts at rest at a specific start position, and moves to rest within a target area. Fitts' law is written:
where MT is the movement time, the time required to complete the motion; ID is the index of difficulty of the task (defined below); and IP is the index of performance. The index of performance is a constant for a specific appendage. The movement time is commonly measured in milliseconds, the index of difficulty in bits, and the index of performance in bits per second.
The index of difficulty was originally defined by Fitts (1954) as
where A is the amplitude of the movement (the distance from the start position to the centre of the target); and W is the width of the target. Both A and W are measured in units of distance (millimetres).
Other formulations for the index of difficulty have been proposed. For example there is the Welford formulation (1960)
currently, the preferred formulation is that proposed by MacKenzie (1989)
This is the preferred formulation because it: always yields a positive index of difficulty, provides a slightly better fit with empirical data than the other formulations, and because it exactly reflects Shannon's Theorem 17, which Fitts' law is based upon.
The GFLMB software allows the experimenter to investigate the application of Fitts' law to the manipulation of a computer input pointing device (such as a mouse). It has been established that Fitts' law provides an accurate and efficacious means to predict the movement time of a pointing device being manipulated by a human operator.
As well as being a research tool, the GFLMB is also useful to educators faced with teaching HCI. The GFLMB allows students to experiment with Fitts' law, and to do their own studies for course projects.
The GFLMB software is available via ftp at:
You will recieve a copy of the manual in text form when
you ftp the GFLMB package from the address given above.
The manual is also available in HTML format at: