Incrementally returning a value based on relative running totals

[salconflu]

I have what has turned out to be a challenging problem. I am trying to model emergence timing of eggs based on cumulative temperature units. When the eggs (Column L) deposited on a given date (Column C) have accumulated 1600 tu's (a running total of Column N) I wish to return the original number (Column L) to a column (Column Q) in Excel. I have also tried returning the date at which cumulative tu's reach 1600 with dget. Unfortunately, I can't figure out how to use Dget or some other function to deal with the relative sums for each value and step through to the next value when the first is returned. I can get the first number by entering the following formula into Column Q, =IF(SUM(N$9:N18)>1600,M$9,0) but I don't know how to increment it once the first value is returned. Any suggestions for approaching this problem would be greatly appreciated.

[Pecoflyer]

Hi and welcome please post a sample sheet ( not a pic) so we can work with it. Thx