[Test-Equipment] Another Bird Termaline Question

[WA5CAB at cs.com]

I have a 500 watt Bird 50 ohm oil filled Termaline load.  How to hook it to 
a transmitter is obvious.  But it has three little solid boxes attached to 
the cone sticking out of one end, with an "N" connector for the source at 
the small end of the cone.  Each of the boxes has a socket for a diode of the 
1N21 style on each box, with one diode plugged in and empty covers sealing 
the other two sockets.  There is an insulated solder lug sticking out of the 
end of each box and a jumper tying the three together.  The boxes are 
stamped 100 W, 500 W and 25 W.  

There is no obvious way to connect an indicator (meter) that I assume would 
indicate watts, other than the crude method of using jumper leads on the 
solder lugs.  Does anyone know whether that was the method intended?  And what 
are the specs on the proper meter?

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480