Calculating difference using previous values

[stxphxe]

Hello,

This is my Data from excel

Excel file

this is the data load editor 

Data load editor

So far i have been able to calculate the standard deviation and average for the values in the chart expressions.

How do i calculate the successive differences, that is the differences between each value for each date. For example, 31/07/2017 will be 929-1079 and so on. i want to  display the results in a table .