Thanks MarkJ. And usually programs like Fugawi and SeaClear make the two an AND condition. In other words for example , Sound an alarm
if the target will pass within 1 mile within the next 15 minutes.
But evidently some programs and chartplotters make them an OR condition which to me doesn't make sense. Who cares about a target that will come within 1 nm but that won't happen for 4 hours.