The RACE RESULT System supports four different passive detection modes:

• First+last detection (default): the decoder stores a first detection based on the value of the reaction time. If the chip stays in the field after this first detection, the decoder will wait for the chip to leave the field for a duration higher than the dead time, and additionally report the last detection before the chip exited the field.
• First detection only: the decoder stores a first detection based on the value of the reaction time. It only stores a new detection for the same chip after the chip has been out of the detection field for a duration higher than the dead time.
• Last detection only: when the chip enters the detection field, the decoder looks for it for the duration of the dead time. When it does not see the chip for a duration higher than the dead time, it stores the last detection before the chip exited the detection field.
• Detection every dt ms: the decoder stores a first read based on the value of the reaction time, then it simply ignores any further reads of the same chip for the duration of the dead time.

First+last detection mode is the default, as it is the one that gives you the most complete information in any situation (a start, a split, or a finish) and lets you pick the right read at software level. First detection only and Last detection only are designed for special cases and should be used with extreme care, e.g. only use the former for a finish or a split timing location, and the latter in a start scenario.

Initially, only the legacy mode Detection every dt ms was available. We recommend not to use it anymore, especially in a start scenario. If a participant stands on the line for a long time before the start, you will typically receive a lot of detections (one every 5 seconds), where you only need the last one. Using this mode, the last detection is unprecise, and if the runner is detected right before the gun fires and leaves the detection field before the dead time is elapsed, you will not have a valid start detection after T0. The new modes came about precisely to address these issues.