Calculation every time a lookup value changes

[C_merr]

Please bear with me as i try to explain what i am looking for. I am trying to calculate something called crush. 1 complete fill is when there are a quantity of 10 "ZS", 9 "ZL", and 11 "ZM". I am trying to create a template so when an order is complete, i will be able to copy and paste a summary into the sheet and it will be able to calculate the crush formula every time the price of "ZS" changes (only focus on "Real Price" the trading platform uses shortcuts so i made a formula to fix this). The hard part is that it is dynamic data. And it isnt always as pretty as completing 1 crush at 10,9,11 quantity. So i need the formula to also calculate the average of ZS,ZL,ZM prices since previous calculation and when the running total of ZS quantity hits another multiple of 10 to calculate crush. In this example crush will be calculated at I9, I12, I17, I20, and I23. Let me know if you need clarification as i expect it. Thank you in advance!

Excel 2012
	A	B	C	D	E	F	G	H	I
8	Order ID	Contract	Price	BuySell	OrderType	Quantity	OakTimeInForce	Real Price	Crush @ fill
9	25496771	ZS	10652	Buy	LMT	10	GTC	10652.5	122.8
10	25496771	ZL	3124	Sell	LMT	9	GTC	3124
11	25496771	ZM	3838	Sell	LMT	11	GTC	3838
12	25496771	ZS	10680	Buy	LMT	10	GTC	10680	Calculate
13	25496771	ZL	3124	Sell	LMT	9	GTC	3124
14	25496771	ZM	3838	Sell	LMT	11	GTC	3838
15	25496771	ZS	10676	Buy	LMT	1	GTC	10677.5
16	25496771	ZS	10680	Buy	LMT	7	GTC	10680
17	25496771	ZS	10682	Buy	LMT	2	GTC	10682.5	Calculate
18	25496771	ZL	3124	Sell	LMT	9	GTC	3124
19	25496771	ZM	3838	Sell	LMT	11	GTC	3838
20	25496771	ZS	10692	Buy	LMT	10	GTC	10692.5	Calculate
21	25496771	ZL	3115	Sell	LMT	9	GTC	3115
22	25496771	ZM	3830	Sell	LMT	11	GTC	3830
23	25496771	ZS	10694	Buy	LMT	10	GTC	10695	Calculate
24	25496771	ZL	3115	Sell	LMT	9	GTC	3115
25	25496771	ZM	3830	Sell	LMT	11	GTC	3830
Sheet1

Cell Formulas
Range	Formula
H9	=IF(B9=$C$1,C9,IF(B9=$B$1,C9,IF(B9=$D$1,IF(RIGHT(C9,1)+0=4,C9+1,IF(RIGHT(C9,1)+0=6,C9+1.5,IF(RIGHT(C9,1)+0=2,C9+0.5,IF(RIGHT(C9,1)+0=0,C9)))))))
I9	=((C10*0.11)+(C11*0.22)-C9*0.1)

 

[C_merr]

If i could talk to excel formula i would try to say...

IF(ZS "real price" is different from previous ZS contract, Averageif(real price,if contract is ZS, CalculatedWhen(the running total of ZS quantity reaches its next multiple of 10 If that makes any sense

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