substract in columns 1

[p658484]

Hello
I would like some helps getting a formula to substract in a column.
I have column a and need the answers as in column b. I have shown the calculation on column c. This is in Cryst 11.
Thank you
a b c
1 10
2 5 -10 a2-a1
3 15 10 a3-a2
4 16 1 a4-a3

 

[lbass]

Your math is incorrect for your first calculation. Anyway, create a formula:

if onfirstrecord or
{table.groupfield} <> previous({table.groupfield}) then
0 else
{table.a}-previous({table.a})

-LB

 

[p658484]

Thank you Ibass. This worked.