Number of records acquired
RecordsAcquired is continuously updated to reflect the number of records acquired since the start function was called. When you issue a start command, the group object resets the value of RecordsAcquired to 0 and flushes the memory buffer.
To find out how many records are available in the buffer, use the RecordsAvailable property. You can also configure the RecordsAcquiredFcn to generate an event each time a particular number of records have been acquired.