Grouped, cumulative total_en.M

// Code written by Hans Peter Pfister, www.powerbi-pro.com
let
    Source = StockMovements,

    Calc_Running_Total = Table.Group(
                                      Source,                                                                           // table as table
                                     {"Product"},                                                                       // key as any
                                                                                                                       // aggregatedColumns as list 
                                        {{"Data",                                                                           // name of new column to be created
                                    // Function Call
                                        (Input as table) as table =>                                                        // data for function
                                        let
                                        Call_Function = fn_cumulative_Total_en(Input),
                                    // End of Function Call

                                        result = Table.FromColumns(                                                         // putting all together
                                                                    Table.ToColumns(Input)&{Call_Function},
                                                                        Value.Type(
                                                                                   Table.AddColumn(
                                                                                                    Input, "Saldo", each null, type number
                                                                                                   )
                                                                                )
                                                                       )
                                        in
                                            result,


                                    type table}}                                                                    // transform into table
                                    ),
    #"Expanded Data" = Table.ExpandTableColumn(Calc_Running_Total, "Data", {"Date", "Amount", "Saldo"}, {"Date", "Amount", "Total"}),
    #"Changed Type" = Table.TransformColumnTypes(#"Expanded Data",{{"Product", type text}, {"Date", type date}, {"Amount", Int64.Type}, {"Total", Int64.Type}})
in
    #"Changed Type"