These superficial levels are termed GN-3 (the most superficial), GN-2 and GN-1 (the deepest level which can yield up selyn without producing sensation if draw speed is slow enough). These donors are often referred to by the title GN-1, GN-2 or GN-3. "She is a GN-1," would indicate that this Gen has worked her way up through the donor levels and might become a candidate to Qualify as a TN-3 (the match for the QN-3, the Third Order Channel.).
This is the key talent discovered in the novel First Channel, that Simes with the Dual selyn transport nervous systems have the ability to adjust their selyn draw-speed and gently take selyn from a Gen so slowly the Gen does not feel any selyn movement. This trick is accomplished by drawing selyn into the channel's Secondary System. When drawing selyn into the Secondary System, a channel is able to stop taking selyn when the channel senses a resistance to selyn flow.
Some Gens can lower their resistance, allowing a channel to draw from the next deeper level of selyn storage.
Each of these levels of storage is given a designation. The most superficial level, the most accessible level which any Gen can tolerate being drained is termed the GN-3 level.
When selyn is taken only from the GN-3 level, very slowly, no selyn movement is felt by the Gen, thus no pain is felt.
A General Order donor can learn to lower resistance at the GN-3/GN-2 barrier, and thus Qualify as a GN-2 donor.
A GN-2 donor can learn to lower resistance at the GN-2/GN-1 barrier and thus Qualify as a GN-1 donor.
A GN-1 donor can also develop enough selyn delivery speed to avoid being burned if attacked by a renSime. A General Order donor who has achieved this ability may be invited to attempt to qualify TN-3, and serve direct personal transfer to a Third Order channel, such as the channels usually employed as Astrogators, though only a small percentage of the GN-1 order donors who attempt this succeed.