In short
Meters report their site, not your exact launch — learn local bias.
Live meters measure where they are mounted — not always the exact corner of the bay you need. Height above ground, sheltering, terrain, and distance from the water all bias a reading. Let alone finding a location which has power, security, maintainability, communications... as the rolling stones said ... "you can always get what you want" ...
Compare a few nearby stations, and learn your spot’s usual offset versus the graph.
