Creating a formula that gives difference between rows

[#1]

Hello everyone, 

I would like to know how to create a formula that checks the differences between the rows.

For example, I have here a file (Data 1) with a column of trials from 1 to 8 (several sequences).

Another column contains the time parameter.

How do I create a new column that checks the time differences between trials 2 and 1, 3 and 2, etc.

Thanks. 

[#2 · Accepted solution]

Based on the provided data, Lag() or Dif() should work

If(:Trial == 1,
	.,
	Dif(:"Time to finish (sec)"n)
)

[#3]

Yes, it works.

Thank you.