This is a measure of the speed of accommodative change. The dioptric accommodative stimulus is alternated between two different levels and the subject reports when a letter target is seen clearly after each alternation in accommodative stimulus. The examiner counts the number of cycles completed in one minute (one cycle being the change from one stimulus level to the other and back again). The standard method of testing accommodative facility is a lens rock procedure using a pair of +2.00D lenses on one side of a flipper bar and -2.00D lenses on the other side. Useful in cases when the patient has visual symptoms which suggest a problem with accommodation but the amplitudes of accommodation are normal.