Optical power difference between the IN port of the D40 board and the OUT/MON port of the M40 board

The MON port of M40 board has 10 dB lower optical power than the IN port of the D40 board and the OUT port of the M40V board.
The split ratio between the MON port and OUT port and that between the MON port and IN port are both 10:90. In other words, the optical power of the MON port is 10 dB lower than that of the IN port. The calculation formula is as follows: Optical power (dBm) of the IN port �?Optical power (dBm) of the MON port = 10 x lg(90/10) = 10 dB.