Abstract: A detection apparatus (1000) enables detection of a substance (116) that may be present on the surface (31, 33) based on measurement of a stream probe signal correlating a substance (116) at least partially obstructing the passage of fluid (30, 35) through a stream probe (500) includes a distal optical gum detector transmission portion (620) and a distal optical gum detector reception portion (720) in a position to transmit and to receive, respectively, an optical signal controlled by a controller (2251), enables the controller (2251) to determine if an open port (526) of a distal tip (522) of the stream probe (500) is in contact with a substance (116) at least partially obstructing the passage of fluid (30, 35) through the open port (526) and not in contact with the gums of a subject or of a user of the detection apparatus (1000) to override false positive signals.

Abstract: The position of a write spot on an optical record carrier, during a write operation by an optical recording device, is important for the quality of the data recorded. Radial positioning of the spot may be facilitated by means of tracking spots, signals from which identify the location of the write spot. Signals from the tracking spots may be affected by the characteristics of the optical record carrier in the their vicinity. Specifically, effects arise from the recorded or unrecorded nature of the tracks adjacent each spot. The invention comprises rotation of the means to generate tracking spots such that tracking spots may be placed in an optimum position for recording, regardless of which data layer on an optical record carrier is to be recorded or the recording direction.