The serial number for the Optima begins with a "B" followed by six (six) numbers.  It can be found on the inside of the 'duckbill' as shown below.

The serial number for the O2Vent Titratable (T) can be found on the inside of the 'duckbill' as shown below.

The serial number for the O2Vent Winged (W) can be found on the inside of the 'duckbill' as shown below.

The serial number for the O2Vent Titratable (T) can be found on the inside of the 'duckbill' as shown below.

The serial number for the O2Vent Winged (W) can be found on the inside of the 'duckbill' as shown below.

The serial number for the O2Vent Titratable (T) can be found on the inside of the 'duckbill' as shown below.

The serial number for the O2Vent Titratable (T) can be found on the inside of the 'duckbill' as shown below.

The serial number for the O2Vent Titratable (T) can be found on the inside of the 'duckbill' as shown below.