O.K. Guys,
What is the difference between all these old. and now newer, competing lighting control techniques... 
To start with, we had the older TTL (through the lens) system. It carried an electrical message from the camera's hotshoe to the strobe via an electrical sync cord. The encoded (different for differing brands)message was delivered to the strobe and told it when to start and quench the flash so that the right amount of light was exposed.
We were then offered TTL via slave sync by S&S in some of their range of strobes..eg, YS90 DUO TTL etc...
This system was said to mimic the light/flash from either internal flash or external strobe that was used as master flash. This system, again mimicked the main flash and was achieved by the strobes slave sensor or fibre optics.
Inon then introduced us to the S-TTL system that was again supposed to mimic the camera's internal strobe.
This was also achieved by slave sensor or fibre optic cable. This system was widely advertised as being extremely accurate and field results seem to support these claims. I should also add that Inon's Z-240 is also wired for the origional TTL system via the electronic sync cord. This system is also capable of 'ignoring' a digital camera's pre-flashes and just firing on the main flash.
Sea and Sea then brought out their version of the S-TTL system and called theirs D-TTL. Once again the strobe moniters for light changes, ignores pre-flashes and mimics the main flash. This strobe, as with the Inon Z-240, is also capable of utilizing the hard wired sync cord.
Now we are offered the Sea and Sea YS 17 strobe that is slave/fibre optic sync cord fired and it is advertised as TTL and NOT D-TTL which is the system that seems to have failed in the YS 110... Is this another new system, the old YS system revamped, or is it the D-TTL system and S&S are too scared to advertise it as such?
So their you have it folks, but what are the differences? All the manufacturers claim that their product produces an accurate exposure but in vastly different ways. It appears to me that all the strobes carefully start and quench with the system that they are mimicking, but Inon claims that their system is the most accurate and S&S claim that their system is different from Inon's yet achieves better results (although from all reports is a failure) and then both systems seem to be basically the same as the origional Slave Sync TTL system offered by the S&S YS series of strobes. I am very confused as to how all these systems work, and not work in the case of the new D-TTL? Can anyone shorten my learning curve and help me sort my way through this "jungle"... 
Thanking you in anticipation guys,
Bruce...
