How to sum cells in one tab and send to cell in another tab PLUS add it to the amount already in the receiving cell

[Christian Panas]

We need to sum the cells for all wholesale orders (let's say for Sourdough Boule) in one Sheets tab and send it to the cell of the production tab, but we want to add those values to an already-existing value (the par) in the cell of the second tab.

Hopefully this helps illustrate:

ORDER TAB

Monday

Customer A: 10 sourdough boule

Customer B: 12 sourdough boule

(sum these and send to the  Monday Sourdough Boule in the Par Tab)

PAR TAB

Monday

Sourdough Boule: 32

(so the 10 + 12 from the ORDER TAB need to be summed and popped into the PAR TAB Monday cell which already has 32 set as the par, resulting in a total of 64)