Locking on the bottom instead of the bar when doing a bar check

When I do a bar check, it will sometimes lock on the bottom instead of the bar, why?. How does it work?

When I do a bar check, it will sometimes lock on the bottom instead of the bar, why?. How does it work? When the Bar Check function is selected, then all echoes are evaluated with reference to the entered Bar depth. However in some cases your bar is emitting a rather faint echo, whereas a strong bottom echo is present, this may lead to a situation where the echosounder uses the strong bottom echo instead of the weak bar. Turn down your TX power, and switch off any TVG action, this may help in regaining an echo from the bar.