The SERVOS page is the interface between the setup "logic" and the real world with servos, linkages and control surfaces. Up to now, we have set up what we want our different controls to do, now is the time to adapt that to the mechanical characteristics of the model.
For each channel, we can define:
A name, that will be shown on the mixer screen when the cursor is on a line belonging to that channel, on the channel monitor and on the failsafe settings page.
An offset or subtrim.
Low and high limits. These are "hard" limits, i.e. they will never be overridden, so as long as they are set so that your servo never forces, it really never will. They also serve as gain or "end point settings", so reducing limit will reduce throw rather than induce clipping.
Center adjustment. This is similar to subtrim, with the difference that an adjustment done here will shift the entire servo throw (including limits), and won't be visible on the channel monitor.
Subtrim behavior: When set to default, adjusting subtrim will only shift the center of the servo throw. Given a -100% to +100% order from the mixer, the servo will still move exactly between the lower and upper limits, without clipping or dead band. This introduces a different stick to servo movement relation for both sides of the stick. Depending on the situation it can be either convenient or problematic, so the = setting has been added to change subtrim effect to rather shift the servo throw "symmetrically". A full throw order from the mixer can now be clipped by the limit that is on the same side as the subtrim, while on the other side the servo will not reach the limit anymore. That way on both sides of the stick a given stick movement always results in the same servo movement. Typically using the default mode allows for faster setup of servos that are driven by a single control input, while = is required to keep correct response of control surfaces using differential and/or mixing several inputs together. The = mode typically requires reducing D/R so that a margin is left between full "control" throw and the defined limits.
The following diagram illustrates the respective behavior of both subtrim modes and how Center adjustment compares to them:
The last line after CH32 is the "Trims to Offsets" function. It is used to take the trims of the currently selected flight mode, transfer their content to the subtrims, reset them, and adjust all other flight modes' trims. If you're close to running out of trim, instead of having to adjust every value one after the other, all it takes is to LONG press ENTER on this line and everything is done magically. Beware that you should still check if it would not be wiser to correct the problem mechanically, especially with large values, as depending on the subtrim behavior setting it might lead to either insufficient and asymmetric throws, or clipping/dead band.