Going from Bottom to top how to check if a cell contains a number, and if it does, then subtract that cell from the next number in the column

[rsd007]

I am looking for formula to find the value in C if value in B column and subtract from the next number in upper B cell and my sheet is keep growing in top as new data is added in top line (27..........).

Thanks for all the help

A	B	C
27​
26​	41​	?
25​
24​
23​
22​
21​
20​
19​	33​	?
18​
17​
16​	9​	?
15​
14​
13​
12​
11​	6​	?
10​	5​	5-29=?
9​
8​
7​	29​	29-10=?
6​
5​
4​
3​	10​	10-40=?
2​
1​	40​

 

[rsd007]

While I am considering that new information, what about the first two questions in my previous post?

List keep growing downwards. More entry every month some time every day. Some days no entry if no body drive.

 

[Peter_SSs]

List keep growing downwards. More entry every month some time every day. Some days no entry if no body drive.

That is not related to what I am asking about. My first 2 questions in post #8 were about XL2BB not working.

In what way is it not working?
At what point in the instructions in the link I provided does the problem occur?

needed other way subtracting 33-41= (-8); 9-33= (-24); 6-9= (-3); 5-6= (-1); 29-5= 24
Also ignore if blank or anything other then number.
Row 2 should be empty as it is the first entry and row 21 should be 29-5=24

Like this?

rsd007.xlsm
	B	C
1
2	41
3
4
5	A
6
7
8
9	33	-8
10
11
12	9	-24
13
14
15
16
17	6	-3
18	5	-1
19
20	X
21	29	24
22
23
Subtract (2)

Cell Formulas
Range	Formula
C2:C23	C2	=IF(ISNUMBER(B2),IFNA(B2-LOOKUP(9E+307,B$1:B1),""),"")

 

[rsd007]

While I am considering that new information, what about the first two questions in my previous post?

That is not related to what I am asking about. My first 2 questions in post #8 were about XL2BB not working.

I thought I also reply to your questions in Post#9.

Like this?

rsd007.xlsm
	B	C
1
2	41
3
4
5	A
6
7
8
9	33	-8
10
11
12	9	-24
13
14
15
16
17	6	-3
18	5	-1
19
20	X
21	29	24
22
23
Subtract (2)

Cell Formulas
Range	Formula
C2:C23	C2	=IF(ISNUMBER(B2),IFNA(B2-LOOKUP(9E+307,B$1:B1),""),"")

Thanks

 

[Peter_SSs]

I thought I also reply to your questions in Post#9.

Post #9 has nothing about why you could not get XL2BB to work