CiDRA Passive Sonar Transmitters - Manual (Page 12)

To use all three levels of access, set the Administrator password first,
log in as Administrator, then set Level 1, and then Level 2.
If any password is set to something other than 0, and others are set to
0, then only the non-zero password will function. If a Level 2
password is first set, you will not be able to log in as an Administrator,
but only read holding registers. In some instances this may be a
desirable mode.
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