Power Query Running_On_hand

Hello, MirageZX 

let
    t1 = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    t2 = Excel.CurrentWorkbook(){[Name="Table2"]}[Content],
    lookup_t = Record.FromList(t2[On_Hand_Qty], List.Transform(t2[Material], Text.From)),
    f = (t as table) => 
        [opening_balance = Record.Field(lookup_t, Text.From(t[Material]{0})),
        pos = List.Buffer(List.Skip(List.Positions(t[Material]))),
        res = List.Buffer(t[Req_Qty]),
        balances = 
            List.Accumulate(
                pos,
                {opening_balance - res{0}},
                (s, c) => s & { s{c - 1} - res{c} }
            ),
        out = Table.FromColumns(Table.ToColumns(t) & {balances}, Table.ColumnNames(t) & {"Running_Stock"})][out],
    gr = Table.Group(t1, {"Material"}, {{"all", each f(Table.Sort(_, "Res_Date"))}}),
    z = Table.Combine(gr[all])
in
    z