Mine

function BTFBOC_Convert(number: string): string; // to one's complement
var i: Integer;
begin
  if number[1] = '1' then
  begin
    result := number[1];

    for i := 2 to Length(number) do
      case number[i] of
        '1': result := result + '0';
        '0': result := result + '1';
        '.': result := '.';
      end;
  end else result := number;

end;

/// why it's works ?
function BTFBTC_Convert(number: string): string; // to two's complement
begin
  if number[1] = '1' then
  begin
    number := BTFBOC_Convert(number);
    result := number; result[1] := '0';
    result := BTFAddition(result, '01'); result[1] := '1';
  end else result := number;
end;