Jitter is a measure of errors in timing. When reading the transition from a pit to a land, there is a timing window that is ideal. The deviation between the window and the transition is important to the reading process. Jitter, as specified by the Orange Book, should be less that 35 nanoseconds. Since jitter can be caused by the player as well as the disc (i.e., the player may incorrectly perceive the transition), it must be measured in relation to a known reference disc.