Toho Electronics TRM20A Operation Manual page 68

Sub record timing
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The sub recorded timing is set. (A sub record alone cannot be recorded. Please confirm it is
previously recording before it records.)
Func key：The sub record begins when the FUNC button is pushed.
System Settings "Device / Other" ⇒ "FUNC key" is "OFF" only when you can choose.
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(Refer to Section 8.18 for "FUNC key".)
Alarm ：The sub record begins when alarm is occurred.
DI ：The sub record begins when the DI input is turned on.
Sync. ：The sub record begins, too, when main record is begun.
OFF ：It doesn't sub record.
DI No.
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This item can only be set when the "
DI No. used for the sub record to begin is set.
Please select arbitrary DI No. from the DI No. selection screen.
Sub record timing" is "DI".
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