What is race numbers and timing in Triathlon?

Section 2: Equipment

Frame geometry: Standard road bicycle with traditional diamond frame. In draft-legal races, no time-trial or triathlon-specific frames are permitted. Seat tube angle and handlebar position must conform to UCI road geometry standards.
Handlebars: In draft-legal races (Olympic, World Triathlon), clip-on aero bars, extensions, and triathlon-specific handlebars are prohibited. Drop handlebars with standard brake levers required. In non-drafting races, aero bars are permitted.
Wheels: Standard road wheels. Disc wheels may be restricted in draft-legal races at the Technical Delegate's discretion (crosswind safety). Wheel diameter: 622 mm (700c) or 559 mm (26 in).
Minimum weight: No minimum weight requirement (UCI's 6.8 kg minimum does not apply to triathlon).
Mechanical condition: Bikes must pass a pre-race mechanical inspection. No loose components, broken spokes, or unsafe modifications.

Wetsuit rules are based on water temperature measured at a depth of 60 cm, taken 1 hour before the race start:

Mandatory: Water temperature below 16°C (60.8°F) for Olympic distance; below 14°C (57.2°F) for sprint distance.
Optional: Between 16–20°C (60.8–68°F) for Olympic distance; between 14–20°C for sprint.
Prohibited: Above 20°C (68°F) for Olympic distance; above 22°C (71.6°F) for sprint distance.
Thickness: Maximum 5 mm at any point. Total coverage must not include gloves, shoes, or full-face coverage.
Swim cancelled: If water temperature falls below 12°C (53.6°F) or exceeds 32°C (89.6°F), the swim may be shortened or replaced with a run segment (duathlon format).

CPSC, CE EN 1078, or equivalent-certified bicycle helmet mandatory.
Helmet must be buckled and secured before the athlete touches or unracks the bicycle in T1.
Helmet must remain buckled until after the athlete has racked the bicycle in T2.
Violation of helmet rules results in a time penalty or disqualification.

Race number: Worn on the front during the run segment and on the back during the bike segment. Race belt permitted for easy switching.
Timing chip: Ankle-mounted transponder provided by the organiser. Must be worn throughout the entire race. Timing mats at swim exit, T1 entry/exit, T2 entry/exit, and finish line record split times.

Frame geometry: Standard road bicycle with traditional diamond frame. In draft-legal races, no time-trial or triathlon-specific frames are permitted. Seat tube angle and handlebar position must conform to UCI road geometry standards.
Handlebars: In draft-legal races (Olympic, World Triathlon), clip-on aero bars, extensions, and triathlon-specific handlebars are prohibited. Drop handlebars with standard brake levers required. In non-drafting races, aero bars are permitted.
Wheels: Standard road wheels. Disc wheels may be restricted in draft-legal races at the Technical Delegate's discretion (crosswind safety). Wheel diameter: 622 mm (700c) or 559 mm (26 in).
Minimum weight: No minimum weight requirement (UCI's 6.8 kg minimum does not apply to triathlon).
Mechanical condition: Bikes must pass a pre-race mechanical inspection. No loose components, broken spokes, or unsafe modifications.

Wetsuit rules are based on water temperature measured at a depth of 60 cm, taken 1 hour before the race start:

Mandatory: Water temperature below 16°C (60.8°F) for Olympic distance; below 14°C (57.2°F) for sprint distance.
Optional: Between 16–20°C (60.8–68°F) for Olympic distance; between 14–20°C for sprint.
Prohibited: Above 20°C (68°F) for Olympic distance; above 22°C (71.6°F) for sprint distance.
Thickness: Maximum 5 mm at any point. Total coverage must not include gloves, shoes, or full-face coverage.
Swim cancelled: If water temperature falls below 12°C (53.6°F) or exceeds 32°C (89.6°F), the swim may be shortened or replaced with a run segment (duathlon format).

CPSC, CE EN 1078, or equivalent-certified bicycle helmet mandatory.
Helmet must be buckled and secured before the athlete touches or unracks the bicycle in T1.
Helmet must remain buckled until after the athlete has racked the bicycle in T2.
Violation of helmet rules results in a time penalty or disqualification.

Race number: Worn on the front during the run segment and on the back during the bike segment. Race belt permitted for easy switching.
Timing chip: Ankle-mounted transponder provided by the organiser. Must be worn throughout the entire race. Timing mats at swim exit, T1 entry/exit, T2 entry/exit, and finish line record split times.