"Ken Wilson" wrote So why can't controller A send a message to Joe and then controller B talks to Bill? Is it because the message might get scrambled if they were both sent at about the same time? ie A sends an instruction but after the "hello, Joe" bit, B sends "Hello,Bill -...." and then the "increase speed to WF7" instruction would get read by Bill and not Joe.
Er Ken, I think some confusion may have crept in here. Handset (or master) A will talk to Joe, whilst B (Slave) talks to Bill, which will go via A... A talks to everyone. B can then change to Fred if it wants, but may be refused if Fred is already under the controll of A, unless the operator of A says yes they can have it... And vice versa for Joe going to A. It's just to avoid someone else taking control of a loco whilst anotehr operator is using it.
At the end of the day, you can control any loco from any handset, so going back to your original H&M and two knobs, yes, it is the same, but you can swap without changing controllers (i.e person A moving his hand onto Knob
2 - etc) and without changing the loco onto the other track\circuit.With the DCC you can even bring in a third loco, (Fred) whilst controller B has left Bill circling the oval (a guess) on his own, so you could either give chase (if the oval is big enough) or shunt on a separate siding.
I hope this is clear and helps you put some of the confusions aside.