Latest day minus previous day

[Sxbbb]

I have a flied RealTime. RealTime is valuable in every day.

I want the RealTime value of the last day minus the previous day in the 'Realyesterday' column.

  EX MM/DD/YYYY   01/02/2023

on 01/03/2023

Or can I do something else that has the same result?

[Sxbbb]

I can't determine if flied number will have the same data. Each day may decrease or increase