Computer_Commando, That is a very good reference.
Does it apply to the question of the OP?
I respectfully disagree.
The manual he has is not for general applications. It is specific to just one product made some time ago. There was no rule that they had to observe conventions used by others. In fact, some other small computer makers at the time made the 9 ping assignments in their own way.
It was chaos.The diagram is consistence with itself.It is for a special cable needed for that particular device. A technician would wire the cable exactly as shown. The cable does not care what you call the wires. The terms Tx and Rx are for reference.
Here is yet another reference that gives modern conventions.
http://www.lammertbies.nl/comm/cable/RS-232.htmlBut what the OP has is old assignment t for just one product.
But it there is any doubt, he needs to test the individual lines and find out what they are.