This read-only Unsigned32 counts the number of synchronization events that have occurred since the test started, per its description. An administrator watches this counter because frequent resynchronizations indicate an unstable link that keeps losing and reacquiring pattern lock, which is itself a sign of trouble even before counting bit errors. For example, a rapidly climbing bertTestStreamMonSyncCounts value on an otherwise 'in-sync' link would alert an operator to intermittent signal problems worth investigating physically.