Push-up Accommodative Amplitude is a fairly standard test to analyze accommodative capability. The tester uses an appropriate accommodative target (usually a letter/word) and pushes it toward the eye until the letter blurs. The distance at which it blurs is considered the near point of accommodation and it can be calculated into diopters of accommodation (amplitude) by dividing the distance into 100 mm or 40 inches. There is also a lens test that can be used to calculate add, called the Plus Build Up (PBU), that simply allows the doctor to put plus in front of the eye to clarity of the target at a fixed distance, often 40 cm/16 in.