If you refer to a balance in a formula, Openbox assumes you mean the closing balance.
So the formula [Senior debt balance]+[Junior debt balance] would give the total debt balance at the end of the period.
If you want to refer to an opening balance, use the BEG (for ‘beginning’) function. In the closing balance formula, you can refer to the opening value for that balance by using BEG() with nothing in brackets. For example, BEG() + [Senior debt drawdowns] – [Senior debt repayments] could be the formula for the senior debt closing balance. Balance formulas must have BEG() in there, or Openbox will give a warning.
BEG([Senior debt]) is the senior debt balance at the start of the period.