def total_velocity_from_pass_diagnostics(diagnostic):
	"""Method for handling a chain_pass diagnostic and outputting it's total velocity

	Shouldn't be calculated for pass chains of 1 pass

	total velocity = total distance / cumulative time
	"""
	total_distance = diagnostic[6]
	elapsed_time = diagnostic[9]
	pass_count = diagnostic[7]

	if pass_count > 1:
		return float(total_distance) / elapsed_time
	else:
		return None