BOAC,
but it is not clear from that 'short' PDF whether a TOW is required before an RTOW can be determined, which is not logical.
As I mentioned earlier, this is the software we use. To determine the RTOW, all parameters (a/c, runway, intersection, wx, bleeds, thrust, flap, CG, etc) except TOW must be entered. It will then calculate the maximum TOW possible for the conditions. If an actual TOW is also provided, then it will calculate the actual performance (N1, speeds, etc) with options for assumed or TOGA. Obviously, if the actual TOW exceeds the max or RTOW it will burp at you.