As part of a continuous effort of reaching the optimal use of the intuitool, a study was conducted to identify the optimal diameter combination between the trackball and the end effector ball. The task was to simulate the end effector movement during an operation, using different diameter combinations. Twenty students performed the trackball-controlling tasks to move the end effector from an initial position to designated circular-shaped targets. The trackball diameters were 19 mm and 40 mm, and those of the end effector balls were 3 mm, 5 mm, and 10 mm. There were four targets: right, left, up, and down. Travel time, accuracy, and trail deviation were measured as independent variables. Accuracy was not a significant factor showing that all participants followed instructions to reach each target as accurately as possible. The time to reach the target depended both on target location and trackball to end effector ratio individually and in their interaction. It was quickest to get to the upper target compared to all other locations. Trial deviation depended only on the target position and the target location and ratio interaction. The performance of going in a straight line was best for the left and right directions as opposed to up and down using the trackball.