Abstract: An apparatus for controlling the effective length of thread wound into a thread package during a winding operation includes a sensor which senses the rotation of a driving roller that drives the package being wound and issues signals representative of the number of revolutions, a divider which divides such signals by a divisor that is selectively adjustable by a user, and a counting arrangement which compares the output of the divider with the desired length of the thread wound into the package as selectively set into the counting arrangement by the user. At least one thread package wound to an actual length with the divisor adjusted to a known value is unwound under conditions that are anticipated to exist during the unwinding of the package by the ultimate user, and the effective length of the unwound thread is measured. The measured value is then used for adjusting the divisor of the divider in the event that the measured effective length deviates from the desired effective length.