How is "slack tide" figured? Is it always a constant like, for example, 45 min. or 1 hr. before and after high and low tide? For example: if high tide is at 12:30am and 12:44pm and low tide at 6:46am and 6:58pm, what would be the times for slack tide? How is it figured? Please email the answer to: firstname.lastname@example.org.