Difference between values in the same column between max and min dates

Hi tangutoori ,

You can achieve it in Power Query Editor, please find the details in the attachment.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("nY5LDoAgDAXvwpqEfgBxqV5CYrj/NSxUcWOMYdWhzMvrcRiGDOjBtrlnnVHfy7oZextCwaEjIBZEMMX+Tu9ZKI6mY+2eBtNK6UlTT2Ngr9ZFiG8l8kldq4T0esucZtduALi6ZVMVh9zL+UNXEt3fejClnA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Concatenate = _t, #"Part number" = _t, #"Change Date" = _t, Value = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Concatenate", type text}, {"Part number", type text}, {"Change Date", type date}, {"Value", Int64.Type}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Concatenate"}, {{"detail", each _, type table [Concatenate=nullable text, Part number=nullable text, Change Date=nullable text, Value=nullable number]}}),
    #"Added Custom" = Table.AddColumn(#"Grouped Rows", "Part numbers", each let 
min = List.Min([detail][Change Date]),
max = List.Max([detail][Change Date]),
result = 
if min=max 
then min
else Text.From(min) & " & " & Text.From(max)
in
result),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Dates", each let 
min = List.Min([detail][Change Date]),
max = List.Max([detail][Change Date]),
minpart = Table.SelectRows([detail],each [Change Date] = min)[Part number]{0},
maxpart = Table.SelectRows([detail],each [Change Date] = max)[Part number]{0},
result = 
if 
min = max
then minpart
else 
minpart & " & " & maxpart
in 
result),
    #"Added Custom2" = Table.AddColumn(#"Added Custom1", "Delta", each let 
min = List.Min([detail][Change Date]),
max = List.Max([detail][Change Date]),
mindvalue = Table.SelectRows([detail],each [Change Date] = min)[Value]{0},
maxdvalue = Table.SelectRows([detail],each [Change Date] = max)[Value]{0},
result = 
if 
mindvalue = maxdvalue
then mindvalue
else 
Number.Abs(maxdvalue-mindvalue)
in 
result),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom2",{"detail"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Removed Columns",{{"Part numbers", type text}, {"Dates", type text}, {"Delta", Int64.Type}})
in
    #"Changed Type1"

Best Regards