EXFO FTB-8500 Series for FTB-500 - Manual (Page 270)

Pattern Tabs
256 FTB-8500 Series and FTB-8120NGE/8130NGE
Pattern RX
Error Analysis
Bit Error: A Bit Error indicates that there are logic errors in the bit stream
(i.e., zeros that should be ones and vice versa).
Mismatch ‘0’: A Mismatch ‘0’ Error indicates a bit error on a binary “0” (for
example ones that should be zeros) found in the test pattern only.
Mismatch ‘1’: A Mismatch ‘1’ Error indicates a bit error on a binary “1” (for
example zeros that should be ones) found in the test pattern only.