Issue with Appsheet formula

[GearStore]

Hi, Hoping I can get some assistance with what I thought was a pretty simple Appsheet formula as follows. In a Field called Sales, I have the Formula:  [Meter] - INDEX(Diesel Dip Entry[Meter],- 1). It's supposed to minus the new meter reading from the reading in the previous row of the same column resulting in the sales. What actually happens is it responds with the same number that is entered in the new field without looking at the previous row. Can anyone please advise on what I'm doing wrong.

Thanks 

[AleksiAlkio · Accepted solution]

You are looking for something like..
[Meter] - LOOKUP(MAXROW("TableName","Timestamp",[Timestamp]<[_THISROW].[Timestamp]),TableName,KeyColumn,Meter)

[GearStore]

Thank you Aleksi. I appreciate the help.

[AleksiAlkio]

You're welcome!