Furuno NX-700A/B - Manual (Page 30)

2. OPERATION
2-10
Protecting message from deleting
Messages are automatically deleted from the memory under the following
conditions.
-66 hours passed from the moment when received.
-Older than No. 200
To prevent a message from being deleted, do the follows;
1. Choose the message at the list display.
2. Press the LIST key to show the list options.
All Messages
Alarm Messages
User Selected Messages
Good Messages
Lock Message
List options
3. Choose Lock Message from the list window.
The protect icon ( ) appears next to the message selected.
Note 1: To unlock a message, choose it and then select Unlock Message in the
list window. (The protect icon disappears.)
Note 2: When you unlock a message which was received 66 hours ago or a
message that is older than No. 200, it will be deleted promptly when
unlocked.
Note 3: Maximum each 50 messages for International and local (or 25% of each
memory) can be protected.