There's a button on the TDC screen, not sure about the location since some mods modify that...
If you place your mouse over it, it should say something like Manual TDC update.
If it's green, is activated, and doesn't matter whether you fire from the peri, UZO or whatever, the systems sticks with that, if is deactivated (RED) the system takes the bearing from the optics being used, range and AoB from the NotePad IF and only IF you check the checkmark on it. That's why you can take your measures, go to the TDC, modify them, and then uncheck the Manual Update, go back to the Peri, and the speed will remain the same as you manually input.
Note: if you click the checkmark after leaving the TDC, the system will update again with what you have on the NotePad
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