The function defines how the pointing device moves. The acceleration, expressed as a fraction, is a multiplier for movement. For example, specifying 3/1 means the pointer moves three times as fast as normal. The fraction may be rounded arbitrarily by the X server. Acceleration only takes effect if the pointer moves more than threshold pixels at once and only applies to the amount beyond the value in the threshold argument. Setting a value to -1 restores the default. The values of the do_accel and do_threshold arguments must be for the pointer values to be set, or the parameters are unchanged. Negative values (other than -1) generate a error, as does a zero value for the accel_denominator argument.
can generate a error.
The function returns the pointer's current acceleration multiplier and acceleration threshold.