Looking to find previous days data without dates

[jg13]

Hello, I have the following table in Power BI,

I am trying to create another column that simply subtracts the current Period Workday's QTD Shipments from yesterday. So for example, in Period Workday 2 I would want 3,567,993. Period Workday 0 is not needed and Period Workday 1 will always stay the same. Period Workday is also a Whole Number data type. I've looked everywhere and can't find a solution to this. If possible, I'd like to be able to do this using a measure and not have to add an index column in my backend.

This is how I want the table to look:

Period Workday	QTD Shipments	Daily Pounds Shipped
1	2,582,394	2,582,394
2	6,150,387	3,567,993
3	8,769,701	2,619,314
4	11,336,278	2,566,577
5	15,017,745	3,681,467
6	15,969,864	952,119
7	19,876,825	3,906,961
8	23,209,836	3,333,011
9	25,905,130	2,695,294
10	29,757,335	3,852,205
11	32,742,357	2,985,022
12	35,744,453	3,002,096
13	38,217,875	2,473,422
14	41,071,749	2,853,874
15	44,965,615	3,893,866
16	47,741,766	2,776,151
17	51,061,310	3,319,544
18	53,881,103	2,819,793

Thank you!

[SamWiseOwl · Accepted solution]

Hi @jg13 

Create a measure like this:
Daily Pounds Shipped =
var DayNum = SelectedValue(table[Period Workday])

var PreviousDayNum = SelectedValue(table[Period Workday])-1

var Previous = Calculate( SUM(table[QTD Shipments]), table[Period Workday] =PreviousDayNum)

RETURN
IF(
DayNum = 1 , SUM(table[QTD Shipments]), SUM(table[QTD Shipments]) - Previous)