Coast Survey reviews charts weekly, and updates the charts with critical corrections. You can see how current your chart is by looking at the chart’s lower left corner. The “corrected through” and “last correction” dates give you the information about the chart’s updates.
When was the chart updated?
The “Last Correction” tells you the effective date of the chart. For instance, “Last Correction: 1/23/2014” means that we have incorporated all chart changes up until January 23.
What information has been included in this version of the chart?
“Cleared through” means that our cartographers have checked the specified Local Notices to Mariners and Notices to Mariners, and have either made appropriate changes to the chart or “cleared” the LNMs and NMs as having no importance to the chart.
You should continually check LNMs and NMs issued after the dates specified on your chart, and manually apply any changes. If you prefer not to make manual updates, you should obtain the latest chart.