Sony DVS-7300 System User Manual page 76

Reentry buttons
To use the output of one M/E bank as a background input to another M/E
bank, press the corresponding button (M/E-1, M/E-2, or M/E-3) at the right
of the bank.
For example, to use the output of the M/E-1 bank as background B on the
M/E-2 bank, press the M/E-1 button in the B row of cross-point buttons in
the M/E-2 bank.
Cross-point button indications
In any row of cross-point buttons, the last button pressed is selected, and
lights. A button which lights red indicates that the signal is being fed to the
corresponding bus, and is forming part of the program output. A button
which lights amber is selected, but the signal is not currently reaching the
program output.
Note
The red and amber color coding thus corresponds to buttons lighting in high
and low tally respectively on some switchers.
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Chapter 4 Basic Operations for Image Creation