Kongsberg M3 Sonar Operator's Manual page 114

M3 Sonar / Operators Manual
Note
104
The M3 recordings are recorded in 1GB volumes, the start of the
volume is .mmb for element raw data or .imb for beamformed data,
the following volumes are sequential numbers .001, .002, .003, etc.
for both type of recordings. It's recommended to select different
folder for source and destination to avoid file name duplications.
922-20007001/1.4