Lightning advice has been updated from the NOAA booklets using reseach results from NSSL as of March 2000. Research around stadiums indicates that a flash to thunder time difference of 30 seconds is necessary lead time to evacuate in advance of a storm. This has evolved into advice stating that if the thunder to lightning delay is 30 seconds or less then people should take cover. However, a distinction is made in the card set which suggests that a 30 second delay represents some threat while a 10 second or less time lag represents imminent danger. This was done in recognition of the fact that most callers will not consider distant thunder as dangerous (a 30 second delay represents thunder so far away that it can barely be heard). Such advice could affect the credibility of the followup advice that the dispatcher gives.