If row exists help

[milesy]

HI Guys

i have a problem that i cant quite work out

i have data such as this

Where A1 is a product code, B1 is the Qty of product allocated and C is the Date the requirement was generated.

I then have a starting position say for example C0005=1000 peices. I want to be able to look at A1 and say if it is the first listing then D=1000-10 peices and of course then the second listing of C0005 would be C0005=990-12

is there a simple way of doing this?



A1 B1 C2
C0005 10 1/1/2018
C0005 12 1/2/2018
C0005 13
C0001 1
C0001 14
C0001 20

 

[Special-K99]

So where are you storing the initial 1000 that Excel would need to do that calculation?