The first thing some people do when they buy a new piece of equipment is study the manual. Others fall back on the old maxim of not reading the instructions until all else has failed. Many of today’s electronic chart plotters will deliver a full breakdown of the tidal height for numerous points on the charts they incorporate, including secondary ports. What bliss that is, but it only works for navigators who’ve taken the trouble to discover which buttons to press. A straw poll shows that a surprising number never bother to find out.